last update: Oct 1, 2009
Italian version

An open source USB programmer for PIC micros, I2C and MicroWire EEPROMs, some ATMEL micros, generic I2C/SPI devices and (soon) other devices

Quick facts
Another programmer?
USB & HID firmware
Control programs
Supported devices
Communication protocol
The circuit
Voltage regulator
How to contribute
Download
History
Links
Contacts

Quick facts

• Completely free and Open Source (including firmware)
• Programs PIC10-12-16-18, 24xxxx I2C EEPROMs, 93SX6 MicroWire EEPROMs, some ATMEL micros, communicates with generic I2C & SPI devices (see supported devices)
• USB 2.0 Full Speed interface, HID class (same as keyboards, mice, etc.)
• Self powered
• Doesn't need drivers
• Built from easy to find components (estimated cost ~10€)
• Hardware generated timings for maximum speed and reliability (writes a 18F2550 in 15s, 8s under Linux)
• Doesn't saturate your CPU and doesn't suffer when other programs are running
• Open source control programs for Linux and Windows

Picture of a prototype:

Another programmer?

In the last few years, as serial and parallel interfaces have almost disappeared, electronics enthusiasts find even more difficult to program microcontrollers; old time programmers don't work any more; common solutions include using USB to serial adapters (which can't accept direct access but only slow API calls), or add-on interface chips, like FTDIxxxx, which appear substantially as serial interfaces and require custom or proprietary drivers.
So why not use PIC controllers and their native USB interface?
After searching a while I couldn't find an USB programmer which was at the same time functional, free, and open source, so I decided to design one.
Open source means that all sources and schematics are given free of charge with the rights to modify and release them.

USB & HID firmware (v0.6.1)

In order to use the USB interface included in some PIC devices we need a firmware that implements one of the classes defined by the USB consortium or a new one; I opted for the HID class, which is supported natively by all operating systems and so doesn't need any driver. Maximum allowed speed is 64K/s, although with my application I measured something in the range 20-40 K/s, certainly enough to program devices with memory of 100K at most.
Like all USB devices this one too has a vid and a pid; these are usually obtained under payment, but since I don't have any money to waste and I'm not selling a commercial product I used the default Microchip vid and a pid of choice: 0x4D8&0x100; anyways it's possible to configure both, so I leave the choice to the user.
The programmer appears to the system as a HID device that exchanges 64 bytes packets every 1 ms.
The USB firmware comes from a nearly unknown open source project, written by Alexander Enzmann, which I modified and adapted to the MCC18 compiler.
I wrote a brief guide on how to use it; to my knowledge this is the only open source firmware with HID support and GPL license.
My programmer code simply adds a command interpreter that drives the microcontroller's outputs according to a set of instructions.
The main control cycle waits for a packet from USB, then executes commands in sequence while managing communication tasks; at the same time a control function is called periodically by a timer interrupt and keeps the DCDC regulator output voltage constant.
Building the project requires only free programs: MPLAB and MCC18 student version, which are unfortunately only available for the windows (in)operating system.
It's certainly possible to compile with SDCC, but some changes are needed to the source code.
Everything is given under the GPL2 license.
Here is the complete MPLAB project, here the hex file only.
Here a version for 18F2450 (with reduced functionality, see the circuit).

Control programs

I initially thought of modifying an existing software, for example winpic or picprog, but I found it would be too difficult because I use packetized communications instead of serial; so I had to write one (two) from scratch.
Unfortunately, or fortunately, since I'm not a professional programmer I kept features at minimum; the linux version doesn't even have a gui (I'm sure many will like that); the result are very small but fast programs that don't use your CPU for nothing.
For most devices the code is verified while programming; for the others immediately following the writing phase.

Linux (v0.6.2)

OP is a command-line executable; it uses device /dev/usb/hiddev0 (or the one specified as parameter) and needs reading rights for it.
eg. >sudo chmod a+r /dev/usb/hiddev0
To permanently enable a user do the following (on Ubuntu and other Debian based distributions, check for others):
as root create a file /etc/udev/rules.d/99-hiddev.rules
if you want to enable a user group write:
   KERNEL=="hiddev[0-9]", SUBSYSTEM=="usb", SYSFS{idProduct}=="0100", SYSFS{idVendor}=="04d8", GROUP="<group>"
where <group> is one of the user groups (to get a list type "groups"); select a suitable group and if your user desn't belong to it execute "addgroup <user> <group>"
or, if you want to enable all users, change reading permissions:
   KERNEL=="hiddev[0-9]", SUBSYSTEM=="usb", SYSFS{idProduct}=="0100", SYSFS{idVendor}=="04d8", MODE="0664"
restart udev to apply changes:
> /etc/init.d/udev reload

If after plugging the device /dev/usb/hiddevX is inexistent (and LED2 doesn't blink at 1 Hz), it's sufficient to execute a few times lsusb to force enumeration, or unplug and replug the cable.
If not otherwise specified the program looks for an USB device with vid&pid=0x4d8:0x100.
Reads and writes hex8 and hex32 files.
Note: optional parameter for -l option must be specified with -l=<file>; it may be a bug of getopt.
Using the -HWtest option and a voltmeter is possible to check that the circuit is working.
To communicate via I2C it's always necessary to specify control byte and address (or addresses); RW bit is handled automatically.
Supported languages are currently English and Italian.

Examples:
> op -h                                               #help
> op -d 18F2550 -ee -s read.hex       #reads code and EEPROM and saves to file
> op -d 16F628 -ee -w write.hex       #writes
> op -i2c_r 8 A0 0                             #reads 8 bytes from I2C bus, control byte A0, address 0

Also included is Hid_test, an utility to send and receive a single 64 bit packet; it can be useful for experimenting with the hardware; in theory one could even write a complete programming script using it.

Download

Windows (v0.6.2)

OpenProg is a C++ application written with Visual C++ 6 and MFC. Using it is straightforward: just connect the programmer, start the application, select the device and read or write; works with XP and the V bloatware.
On the "Device" tab it's possible to modify some programming options, such as ID and calibration write, use of eeprom etc.
The "I2C/SPI" tab is useful for communicating with generic I2C and SPI devices; in case of I2C it's always necessary to specify the control byte (and address, if not zero); RW bit is handled automatically.
For example to write manually 3 bytes on a 24xx16 at address 64 write: A0 40 1 2 3
Using the "Hardware Test" function and a voltmeter is possible to check that the circuit is working.
I didn't include an installer since there aren't any libraries and the executable is very small.
It accepts hex8 and hex32 files; supported languages are currently English and Italian; it's possible to add a resource file with other languages.
Command-line options are:
-d <device> , selects a target
-r <file name> , reads the target and writes to file
-w <file name> , writes a file to the target
-gui , do not exit after writing or reading (only if -w or -r are specified)

A screenshot of OpenProg:


Download application ... and sources (Visual Studio 6 workspace)

It may be of interest the fact that the DDK (driver development kit) is not required for compilation; I link explicitly to the system library hid.dll and manually load the functions needed.

Supported devices

I tried this programmer with a small number of devices (those I own) indicated in bold; the other devices are supported but not tested.
Please let me know if you verify operation with these devices.
Also contact me if you need other algorithms or code new ones by yourself.

devices supported for read and write:
10F200, 10F202, 10F204, 10F206, 10F220, 10F222,
12F508, 12F509, 12F510, 12F519, 12F609, 12F615, 12F629, 12F635, 12F675, 12F683,
16F505, 16F506, 16F526, 16F54, 16F610, 16F616, 16F627, 16F627A, 16F628, 16F628A, 16F630, 16F631, 16F636, 16F639, 16F648A, 16F676, 16F677, 16F684, 16F685, 16F687, 16F688, 16F689, 16F690, 16F716, 16F73, 16F737, 16F74, 16F747, 16F76, 16F767, 16F77, 16F777, 16F785, 16F818, 16F819, 16F83, 16F83A, 16C83, 16C83A, 16F84, 16C84, 16F84A, 16C84A, 16F87, 16F870, 16F871, 16F872, 16F873, 16F873A, 16F874, 16F874A, 16F876, 16F876A, 16F877, 16F877A, 16F88, 16F882, 16F883, 16F884, 16F886, 16F887, 16F913, 16F914, 16F916, 16F917, 16F946,
18F242, 18F248, 18F252, 18F258, 18F442, 18F448, 18F452, 18F458, 18F1220, 18F1230, 18F1320, 18F1330, 18F2220, 18F2221, 18F2320, 18F2321, 18F2331, 18F2410, 18F2420, 18F2423, 18F2431, 18F2439, 18F2450, 18F2455, 18F2458, 18F2480, 18F2510, 18F2515, 18F2520, 18F2523, 18F2525, 18F2539, 18F2550, 18F2553, 18F2580, 18F2585, 18F2610, 18F2620, 18F2680, 18F2682, 18F2685, 18F4220, 18F4221, 18F4320, 18F4321, 18F4331, 18F4410, 18F4420, 18F4423, 18F4431, 18F4439, 18F4450, 18F4455, 18F4458, 18F4480, 18F4510, 18F4515, 18F4520, 18F4523, 18F4525, 18F4539, 18F4550, 18F4553, 18F4580, 18F4585, 18F4610, 18F4620, 18F4680, 18F4682, 18F4685,
2400, 2401, 2402, 2404, 2408, 2416, 2432, 2464, 24128, 24256, 24512, 241025,
93C46C, 93C56C, 93C66C, 93S46, 93S56, 93S66
AT90S1200, AT90S8515, AT90S8535, ATmega8, ATmega8A, ATmega8515, ATmega8535, ATmega16, ATmega16A, ATmega32, ATmega32A

devices supported for read only:
12C508, 12C508A, 12C509, 12C509A, 12C671, 12C672, 12CE673, 12CE674

Communication protocol

To design a communication protocol we must take into account some often contrasting requirements:
transfer speed and efficiency, code size, adaptability and expandability.
At one end we find simple serial programmers, which only take commands to change voltage levels; host software manages both timings and programming algorithms, but needs all the CPU time and is dramatically affected by other processes running on the system.
At the other extreme are "smart" programmers, which autonomously manage timings and algorithms, but must be updated to support new devices.
I chose a combination of both: ICSP (In Circuit Serial Programming) commands are implemented in firmware, but host software manages the algorithms.
In order to increase speed and efficiency some instructions correspond to sequences of frequently repeated commands, such as sequential reads.
The advantage of this approach is that timings are very precise, while the extreme variety of algorithms does not increase the firmware code size.
For example, this is the sequence used to enter program mode for 16F628 and read DevID:
    SET_PARAMETER;    //set delays to be used by other instructions
    SET_T1T2;                    //T1 & T2
    1;                                     //T1=1us
    100;                                 //T2=100us
    EN_VPP_VCC;             //Vpp & Vcc = 0
    0x0;
    SET_CK_D;                 //Clock and Data as output and 0
    0x0;
    EN_VPP_VCC;            //Vpp enabled
    0x4;
    NOP;                              //Small delay
    EN_VPP_VCC;            //Vdd+Vpp enabled
    0x5;
    NOP;                             //Small delay
    LOAD_CONF;             //program counter to 0x2000
    0xFF;                             //fake config
    0xFF;                             //fake config
    INC_ADDR_N;          //increment address by 6
    0x06;
    READ_DATA_PROG; //read DevID
    ...

In addition to ICSP commands other instructions manage the programmer, control programming voltages, execute precise delays, communicate via I2C or SPI bus.
Every instruction is executed in at least 40 us, due to the interpreter loop execution time; ICSP commands use T1 or T2 as values for delays; all instructions return an echo, with the exception of FLUSH, which immediately sends the output buffer and stops the execution of current packet; in case an instruction doesn't have enough parameters it returns an error (0xFE) and the execution of current packet is halted.
The state of USB connection is signaled by LED2: it blinks at 4 Hz during enumeration, at 1 Hz in normal operation.
LED1 shows when there are instructions being executed.
Following is the list of all instructions:

Instruction	Value	Parameters	Answer	Notes
NOP	0x00	none	echo	no operation
PROG_RST	0x01	none	echo + 10B	programmer reset; sends fw version (3B), ID (3B), " RST" string
PROG_ID	0x02	none	echo+ 6B	sends fw version (3B), ID (3B)
CHECK_INS	0x03	1B	echo + 1B	if specified instruction exists returns its code, otherwise returns error (0xFE)
FLUSH	0x04	none	none	flushes output buffer (sends 64B) and stops command interpreter for the current packet.
VREG_EN	0x05	none	echo	turns on the voltage regulator
VREG_DIS	0x06	none	echo	turns off the voltage regulator
SET_PARAMETER	0x07	1B	echo	sets internal parameters; byte1: parameter to change, byte 2-3 value: SET_T1T2 (=0):      T1 &  T2 SET_T3 (=1):           T3(H,L) SET_timeout (=2):    timeout(H,L) SET_MN (=3):         M, N
WAIT_T1	0x08	none	echo	waits T1 us (1us default)
WAIT_T2	0x09	none	echo	waits T2 us (100us default)
WAIT_T3	0x0A	none	echo	waits T3 us (2ms default)
WAIT_US	0x0B	1B	echo	waits N us
READ_ADC	0x0C	none	echo +2B	reads regulator voltage (effective 10bits, MSB-LSB); considering the input divider, voltage in V is <value>/1024*5*34/12
SET_VPP	0x0D	1B	echo +1B	sets regulator voltage to <parameter>/10; if error is < 200 mV within 15ms returns <parameter>, otherwise error (0xFE)
EN_VPP_VCC	0x0E	1B	echo	controls Vpp and Vcc on the programmed device; bit 0: Vcc, bit 1: Vpp; bit 2 and 3: control line impedance: keep at 0
SET_CK_D	0x0F	1B	echo	controls CK, D, PGM on the programmed device; 1 bit for level (0-1), 1bit for impedence (low-high); bit 0-1: D, bit 2-3: CK, bit 4-5: PGM
READ_PINS	0x10	none	echo +1B	reads the state of control lines, 1 bit level (0-1), 1bit impedence (low-high); bit 0-1: D, bit 2-3: CK, bit 4-5: PGM
LOAD_CONF	0x11	2B	echo	ICSP command: Load configuration (000000), T1 us between command and data; 14 bit data (right aligned, MSB-LSB)
LOAD_DATA_PROG	0x12	2B	echo	ICSP command: Load Data in Program Memory (000010), T1 us between command and data; 14 bit data (right aligned, MSB-LSB)
LOAD_DATA_DATA	0x13	1B	echo	ICSP command: Load Data in Data Memory (000011), T1 us between command and data; 8 bit data
READ_DATA_PROG	0x14	none	echo +2B	ICSP command: Read Data from Program Memory (000100), T1 us between command and data; 14 bit data (right aligned, MSB-LSB)
READ_DATA_DATA	0x15	none	echo +1B	ICSP command: Read Data from Data Memory (000101), T1 us between command and data; 8 bit data
INC_ADDR	0x16	none	echo	ICSP command: Increment Address (000110), T1 us delay at the end
INC_ADDR_N	0x17	1B	echo	ICSP command: Increment Address (000110), T1 us delay at the end; repeated N times
BEGIN_PROG	0x18	none	echo	ICSP command: Begin Programming (001000)
BULK_ERASE_PROG	0x19	none	echo	ICSP command: Bulk Erase Program Memory (001001)
END_PROG	0x1A	none	echo	ICSP command: End Programming (001010)
BULK_ERASE_DATA	0x1B	none	echo	ICSP command: Bulk Erase Data Memory (001011)
END_PROG2	0x1C	none	echo	ICSP command: End Programming (001110)
ROW_ERASE_PROG	0x1D	none	echo	ICSP command: Row Erase Program Memory (010001)
BEGIN_PROG2	0x1E	none	echo	ICSP command: Begin Programming (0011000)
CUST_CMD	0x1F	1B	echo	ICSP command specified in the parameter
PROG_C	0x20	2B	echo +1B	Programs a word following 12Cxxx algorithm: 000010, 001000, 001110, M pulses & N overpulses
CORE_INS	0x21	2B	echo	PIC18 ICSP command: Core instruction (0000); 16 bit data (MSB-LSB)
SHIFT_TABLAT	0x22	none	echo +1B	PIC18 ICSP command: Shift TABLAT (0010); 8 bit data
TABLE_READ	0x23	none	echo +1B	PIC18 ICSP command: Table read (1000); 8 bit data
TBLR_INC_N	0x24	1B	echo+N+NB	PIC18 ICSP command: Table read post-inc (1001); 8 bit data; repeats N times; returns N and NB data
TABLE_WRITE	0x25	2B	echo	PIC18 ICSP command: Table write (1100); 16 bit data (MSB-LSB)
TBLW_INC_N	0x26	(2N+1)B	echo	PIC18 ICSP command:  Table write post-inc (1101); 16 bit data (MSB-LSB); repeats N times (N is the first parameter)
TBLW_PROG	0x27	4B	echo	PIC18 ICSP command: Table write and program (1111); 16 bit data (MSB-LSB); also executes a NOP with a delay specified in  parameters 3-4 (in us)
TBLW_PROG_INC	0x28	4B	echo	PIC18 ICSP command: Table write and program post-inc (1110); 16 bit data (MSB-LSB); also executes a NOP with a delay specified in  parameters 3-4 (in us)
SEND_DATA	0x29	3B	echo	PIC18 ICSP command specified in byte 1; sends 16 bit data (MSB-LSB)
READ_DATA	0x2A	1B	echo+1B	PIC18 ICSP command specified in byte 1; reads 8 bit data
I2C_INIT	0x2B	1B	echo	Initializes I2C communication: 0xFF disables I2C; bit 6: slew rate control for speed > 100kbps; bit 5:3 speed: 0=100k, 1=200k, 2=400k, 3=800k, 4=1M; attention: use pull-up resistors according to selected speed; bit 2:0: logic level of A2-A1-A0 (on device)
I2C_READ	0x2C	3B	echo+1+NB	Reads <parameter 1> bytes from I2C bus using <parameter 2> as control byte and <parameter 3> as address; forces automatically the RW bit in the control byte. Responds with <parameter 1> + Data or with ACK_ERR (0xFD) in case of acknowledge error (eg. if there are no devices on the bus)
I2C_WRITE	0x2D	3B+NB	echo	Writes <parameter 1> bytes to I2C bus using <parameter 2> as control byte and <parameter 3> as address; forces automatically the RW bit in the control byte. Responds with ACK_ERR (0xFD) in case of acknowledge error (eg. if there are no devices on the bus). For 2 byte addresses just use the 2nd byte of address as the first byte of data.
I2C_READ2	0x2E	4B	echo+1+NB	Reads from I2C bus; identical to I2C_READ, but uses 2 bytes for addressing
SPI_INIT	0x2F	1B	echo	Initializes SPI communication: 0xFF disables SPI bit 1:0 speed: 0=100kbps, 1=200kbps, 2=300kbps, 3=500kbps bit 2:3 SPI mode
SPI_READ	0x30	1B	echo+1+NB	Reads <parameter 1> bytes from SPI bus. Returns <parameter 1> + Data; If <parameter 1>=0 returns the byte that was last received (during either read or write)
SPI_WRITE	0x31	1B+NB	echo+1B	Writes <parameter 1> bytes to SPI bus.
EXT_PORT	0x32	2B	echo	Forces levels of communication ports: <parameter 1> = <RB7:RB0> <parameter 2> = <RC7,RC6,RA5:RA3> Does not change signal direction.
AT_READ_DATA	0x33	3B	echo+1+2NB	ATMEL command: read program memory (0010H000); reads <parameter 1> words at address <parameter 2> : <parameter 3> via SPI. Returns <parametro 1> + Data
AT_LOAD_DATA	0x34	3B+2N	echo+1B	ATMEL command: load program memory page (0100H000); loads <parameter 1> words at address <parameter 2> : <parameter 3> via SPI. Returns <parameter 1>
CLOCK_GEN	0x35	1B	echo	Generates a clock signal on RB3 (using CCP1-2 and TIMER1) bit 2:0 frequency: 0=100kHz, 1=200kHz, 2=500kHz, 3=1MHz, 4=2MHz, 5=3MHz, 6=6MHz; Disables PWM1 output (DCDC regulator)
SIX	0x36	3B	echo	PIC24 ICSP command: Core instruction (0000); 24 bit data (MSB first) (Experimental)
REGOUT	0x37	none	echo +2B	PIC24 ICSP command: Shift out VISI register (0001); 16 bit data (Experimental)
ICSP_NOP	0x38	none	echo	PIC24 ICSP command: Execute NOP (0000) (Experimental)
TX16	0x39	1+2NB	echo+1B	Transmits 16 bit words over ICSP; N*16 bit data (MSB first) (Experimental)
RX16	0x3A	1B	echo+1+2NB	Receives 16 bit words over ICSP; N*16 bit data (MSB first) (Experimental)
uW_INIT	0x3B	none	echo	Initializes MicroWire communication
uW_TX	0x3C	1B+NB	echo+1B	Writes <parameter 1> bits to MicroWire bus. Data is specified MSB first
uW_RX	0x3D	1B	echo+1+NB	Reads <parameter 1> bits from MicroWire bus. Returns <parameter 1> + Data, MSB first
READ_RAM	0xF0	2B	echo+3B	Reads from host memory; 16 bit address, 8 bit data; echoes address
WRITE_RAM	0xF1	3B	echo+3B	Writes to host memory; 16 bit address, 8 bit data; echoes address and data
LOOP	0xF2	none	none	Resets instruction pointer and executes all instructions again. For test purposes only.

The circuit (v1.4)

The project is based on a 28 pin 18F2550, but only about a third of the memory and 0% of eeprom was used, so it will fit confortably into the smaller 2455.
The 2458 and 2553 have a 12 bit ADC, so should work as well.
With some modifications I adapted the code to the 2450; since this model lacks the MSSP module I used a software implementation of I2C and SPI; it also lacks the second PWM channel, therefore it can't generate the clock for Atmel chips (for those that are configured for external clock); in this case RB3 can be used to turn on an external oscillator (which would be inserted in a modified Atmel expansion board).
The use of the corresponding 40 pin devices (4450, 4455, 4458, 4550, 4553) requires modification of the PCB.
In order to implement an USB pheripheral with a PIC micro we need very few components: the main microcontroller, a quartz, some capacitors, and a USB type B receptacle, exactly as written in application notes from Microchip.
To be able to program PIC devices we need two digital lines for clock and data and two supply voltages, VCC and VPP, which are controlled using three transistors; VPP comes from a switching voltage regulator that requires an additional transistor and is described later.
The basic circuit and PCB can host PIC devices with 8, 14, 18, and 20 pins (except 10Fxxx); they should be inserted in U3 with alignment to pin1:



I plan to make an adapter for 10Fxxx with 6 or 8 pins; in the meantime it's possible to get by using wires.
I2C memories go in U4.
Other devices can be programmed using expansion boards plugged to connectors CONN2-3:

• 28-40 pin PICs + ICSP connector
• 8-20 pin PICs (same as main board, but there's more space for a ZIF socket) + ICSP conn.
• I2C, SPI, uW memories and I2C-SPI conn.
• 8-14-20-28-40 pin ATMEL micros and I2C-SPI conn
• ST72 (future)

Of course they're not required for basic operation.

Pin mapping of various connectors in the base and expansion boards:
Expansion1(micro side): RB7-RB0,RC7,RC6
Expansion2: RA3-RA5,RA2,RA1,RE3,VDD,GND,VPPU,VDDU
ICSP: VPPU,VDDU,ICD,ICK,GND
ICSP-IN: VPPU,VDDU,ICD,ICK,GND (not the same as ICSP; with this you can program the main micro without extracting it)
I2C/SPI: CK,DI,DO,GND (I2C doesn't need DO)

Map of resources used:

Pin	Various functions	ICSP	I2C-EEPROM	SPI-EEPROM	SPI-ATMEL	uW-EEPROM
RB7		PGM
RB6		ICSP clock
RB5		ICSP data	A2			W (6)
RB4			A1	HLD		S (1)
RB3			A0	CS	Device clock	PRE (7)
RB2	expansion
RB1			Clock	Clock	SPI Clock	Clock
RB0			Data	Data out (MOSI)	Data out (MOSI)	Data out
RC7				Data in (MISO)	Data in (MISO)	Data in
RC6			WP	WP	RESET
RC5	USB D+
RC4	USB D-
RC2	DCDC PWM
RC1	controls VDD
RC0	controls VPP
RA5	expansion
RA4	expansion
RA3	expansion
RA2	LED 2
RA1	LED 1
RA0	ADC for regulator
RE3	S1 switch

Schematic diagram of base module:



PCB of base module:


Many components are optional, like expansion connectors CONN2-3, protection resistors R11:23 (considering their cost why not use them?), I2C pull-up resistors R26-27, S1 switch, ICSP-IN CONN4 (right now it's used to program the main microcontroller without extracting it).
The pcb was optimized to fit the solder side, however a few jumpers are needed on the component side; if you want you can avoid that by using a double side pcb. Pay attention to the orientation of transistors: Q1's emitter to the left, Q2 up, Q3 and Q4 right.
In assembling the adapters I suggest to insert the expansion connectors from the component side, and keep their plastic spacer on that side; this improves the solder strength, especially during extraction.
To verify that everything is working correctly use the "Hardware Test" function in the control program: you have to check that the voltage at VDD, VPP, CK, D, PGM (on U3) corresponds to what you read on screen.

Component list:
U1 12Mhz quartz (also 4, 8, 16, 20; reconfiguration of input divider options required)
U2 18F2550 (also 2450,2455,2458,2553,4450,4455,4458,4550,4553)
U3 20p socket.
U4 8p socket.
Q1-2 BC557 (or any PNP, pay attention to polarity)
Q3-4 BC547 (or any NPN, pay attention to polarity)
D1-2 LED
D3 1N4148 (or any diode, better if Shottky)
L1 100uH resistor type or other
R1 22K
R2 12K
R3 100K
R4:6 10K
R7 1M
R8-9 2.2K
R10 10K
R11:23 100
R24-25 300K
R26-27 10K
C1 22-100uF 25V
C2-3 22pF
C4 >= 220nF
C5 100nF
C6 10uF
C7-8 100nF

The schematic diagram was drawn with Gschem, an open source program that comes with GEDA suite.
In their website it's not evident (as they all use linux), but it's also possible to run the program in windows under cygwin; I suggest to use the latest version (you need to compile sources).
PCBs were drawn with PCB; in this case there is also a (somewhat limited) windows version.
With a little effort the circuit can also be mounted on experimental boards, without pcb.

Schematic diagram of base module: .pdf, .png; expansion boards: .pdf, .png; everything in gschem format: Oprog.sch
Pcb of base module: .pdf, .png; base module + expansion boards: .pdf, .png; everything in PCB format: Oprog.pcb
Complete archive., includes sources, gerber, pdf, png

How to program the main micro the first time?

This is an interesting problem: a new device can't work as programmer, so it must be programmed in some way.
Apart from asking someone else to do it for you, my advice is to build one of  those serial programmers, like JDM, to do the job the first time.
It may seem strange to use a programmer to build another one, but there is no way to interface USB without firmware; I think the effort is worth it because serial programmers are not very reliable, are slow, and of course not portable to new computers that lack serial ports.
It would also be a good idea to buy a backup micro, in order to program it with updated firmware versions.


The main circuit and some expansion boards (8-20p PIC with ZIF, 28-40p PIC, ATMEL, EEPROM):

Switching voltage regulator

In order to generate a voltage higher than 5V we need a boost switching converter.
On the market there are thousands of single chip solutions, but I used instead the microcontroller itself and a few external components.
The width of output pulses will vary to keep the output voltage stable over all operative conditions.
In practice this is a digitally controlled regulator, as shown in the following diagram:



The ADC converter presently uses the 5V supply as a reference, so the output voltage will follow it; it is possible to connect an external reference to RA3 to improve the overall precision.
Switching frequency is 90 kHz, which is well over the cutoff frequency of the output LC filter (~2,3 kHz).
The performance is limited by losses due to the transistor, diode, inductor, but since the load is very low we can use low-cost (even recycled) components; to improve load capability switch to a better transistor, a Shottky diode, a higher rated inductor.
Anyways, in order to design a suitable regulator (block C above) it's necessary to work in s domain and model the converter itself; this has fortunately been done already, some info is available for example here.
With present component values the boost converter operates in dicontinuous mode; critical current is:
Icrit=Vu*T/(16*L)=86 mA
well over expected load, supposed to be 1 mA.
Other parameters:
Vi=5
Vu=12.5
D=(Vu-Vi)/Vo
L=100e-6
C=47e-6
I=1e-3
R=12/I
Rl=1.6 (inductor series resistance)
T=1/90e3

Transfer function results to be:
Which has the following Bode diagram:


It seems that the system, in closed loop, would be stable even by itself; however it would have a steady state error of 1/DCgain.
It's better to use a controller with a pole on the origin and a zero to stabilize everything, for example the following controller:

Overall transfer function would be:
The system is stable, with a phase margin of ~75º.
Since we operate in the digital domain we must choose the sampling frequency.
It can't be too high because of execution speed; if too low it limits the regulator bandwidth; a period of 250 us was a good compromise.
The various transfer functions are converted to z domain using bilinear transformation:
The controller is:
Remember that z^-1 represents a delay of one clock cycle.
Next we must deal with quantization and calculation errors.
A/D converter is 10 bits wide, and is triggered by timer2; at the end of conversion an interrupt calls the regulation routine, which calculates the new duty cycle for the PWM peripheral, also 10 bits wide.
On the feedback path it's necessary to include a voltage divider in order to limit ADC input voltage to [0,5V]; R1 and R2 do this.
So the block diagram is modified as follows:


a=12/34

Vu=C'H(Vi-aVu)
To compare with the previous model we can multiply both terms by a; simply remembering to change the set point we can decide that the new input is Vi/a, and equate with the previous expression:
aC'=C
aC1'=C1
aC2'=C2

Since the hardware works with 10 bit digital data we can go from D/err to pwm/[err]:

[err]=err*1024/5
pwm=D*1024
pwm(1 - z^-1)=[err](5*C1/a - 5*C2/a z^-1)=[err](3.564 - 3.52 z^-1)

It's clear that integer multiplications can't be used with these coefficients; the easiest solution is to work with fractional values (i.e. divide output by 2^N and multiply coefficients accordingly); considering that pwm output is 10 bits wide and left-aligned, we can easily work with values divided by 64.

pwm(1 - z^-1)=[err](k1 - k2 z^-1)/64

k1=5C1/a*64=228.12 ~ 228
k2=5C2/a*64=225.25 ~ 225

Following are step responses of continuous-time system (blue), discrete-time system (red), discrete-time system with approximate cefficients (green); As you can see they're almost coincident.

For all calculations I used Octave, an open source mathematical modeling tool; version 3 has just been released, and it can be used also under the famous windows (almost)operating system.
If someone is interested these are the modeling scripts I used.
The real code for the control function was written in assembly; this is necessary for performance reasons.
In fact our C compiler calls a library function to perform multiplications, so it has to save many variables on the stack causing a delay; in this case the resulting execution time had reached 50 us, which is a significant fraction of the sampling period.
Instead, by avoiding function calls and manually coding the 16x8 bit multiplication (see k1 & k2), the execution time is down to 12 us.

Some real waveforms:

 
Power-up transient, 50 ms/div


Step response to load change (load on top trace, AC coupled output on bottom tr.), 50ms/div


Step response to set point change (from 11,5 to 12,5 V), 50 ms/div

How to contribute

The best way to contribute to this project is to build it, use it, and report bugs or suggestions.
Also there are still many devices to test; check the list in supported devices.
Whoever has the know-how and patience can also expand support to other devices.
I'm looking for volunteers to build a linux gui, in particular somebody familiar with QT.
If you find this project useful write me a couple of lines: , and if you modified it show me your work.

Downloads

Schematic diagram and pcb: complete archive.
Firmware: complete MPLAB project or compiled firmware (.hex) or a version for 18F2450 (with reduced functionality, see the circuit).
OP (Linux)
OpenProg (windows): application only;   sources (Visual Studio 6 workspace)
Octave scripts

History

a long time ago:     need for a reliable and free USB programmer
2007:                    experiments with USB PIC and varionus firmwares; voltage regulator
2008:                    first prototypes and software
july 2008              documentation and website, released version 0.3
august 2008          version 0.4, added support for I2C EEPROMs
november 2008     version 0.5, I2C & SPI bus, added some ATMEL devices
january 2009         control progs v0.5.1, added some PIC devices, removed some bugs
march 2009           control progs v0.5.2 and v0.5.3, added some PIC an Atmel devices, removed some bugs
april 2009             schematic diagram and pcb v1.4
june 2009              version 0.6, fully GPL2 USB firmware, added support for 93Sx6 MicroWire EEPROMs
september 2009     version 0.6.1, solved some SPI bugs, added support for some Atmel devices and 93Cx6C
october 2009        control progs v0.6.2, bugfix
the future              increase support for PIC and ATMEL micros (as soon as I can get free samples); add PIC24, dsPIC, ST72, SPI EEPROM, JTAG; compile firmware also with SDCC; use a common framework for win and linux GUI

Links

USB 2.0 standard
HID page on USB.org
Quick guide to a HID firmware
USB Central
USB & PIC
Microchip
Atmel
hiddev documentation
Winpic
ICprog
Octave
GEDA-Gschem
PCB
GNU/GPL
USBPicprog, another open source programmer

Contacts

For informations or comments:
Alberto Maccioni  

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