Electronics > Open Source Hardware

OSHW Universal Programmer design proposal

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I was thinking about what it would take to make a really good OSHW Universal Programmer. I came up with this for the hardware part:


* Cheap to make
* Easy to make
* Maximum flexibility - universal pin drivers, scaleable in groups of 8 up to 48 or so
* No FPGA / CPLD with hostile licensing policies
* No programmer required to avoid the chicken-egg problem
* Powered by a cheap wall socket adapter (24V/1A or so)
* Programmable logic threshold levels, including 1.8V logic
* Two programmable power rails for Vpp and Vcc that could support up to 25V (supply permitting) and some ~200mA, with 0.1V resolution, and programmable logic thresholds (Voh, Vih, Vil) - controlled by simle 8bit R-2R DACs driven by shift registers
* USB connection, Full speed bulk mode transfer to enable fast programming. May use special driver or CDC serial port emulation or both. No HID (too slow)
* Hardware interface specified at USB level so people can write drivers for unsupported operating systems
* 160x100 mm board size limit so I can use my Eagle hobbyist edition to do it
* Preferably single sided boards
Because I want so complex pin drivers which means board space, I would have to split the design in several boards that stack on top of each other:

* Base board - with ATmega32U4, USB, power supplies
* Variable number of Pin driver boards, each with 8 pin drivers. You can have 1-6 of them, all identical. Stacks with 180 degree rotation to enable use of simple pinheaders/receptacles instead of expensive board to board stacking connectors or two sided baord/smt headers
* Socket board on top with 40 pin ZIF, ISP or JTAG connectors, whatever is needed.
All these would be put together with standoffs to form a big brick :)

ATmega32U4 has native USB support for full speed mode, and has factory programmed bootloader (USB-DFU) that solves the initial programming problem.

For pin drivers, I came up with fairly complex but still cheap design with shift registers, 1 to 8 latching decoders (74hc237) and some discrete transistors, and a simple variable threshold logic probe for each pin made of two comparators.
Each pin can be in one of 8 states - GND/Low, Vpp (programmable), Vcc (programmable), High (programmable), Pullup to High, Pulldown, Clock (programmable level and frequency) and input. Each pin can be read thru 3 different bits - one is simple TTL level input (fast, but fixed thresholds), and two input comparators (lm339n) that detect if pin is over High input threshold (programmable) or under Low threshold (programmable). Pins are floated thru 1M resistor to a voltage between High and Low to detect undrvien pins for the logic probe input mode (this logic probe is rather slow because fast comparators are too expensive).
Pin output state (3bits) and pin read bits (3bits) are chained using 6 serial shift registers (74hct164, 74hct166). One output chain will be connected to input chain on the socket board to provide for autodetection of number of pin driver boards.

Everything except the ATmega32U4 would be in thru hole packages to make it easy to build by hand.

As this will be pretty big brick there is no point in USB only powered mode sorry :) No way to make it much smaller with discrete pin drivers and cheap.

It shoud be fast enough for programming parts at maximum speed, probably too slow to use as a logic analyzer. But you could maybe plug in a LCD display into this and test it ;)

I like your idea. Why not use smd stuff? the 74hc237 could be a so16, maybe transistors could also be smd. In this way it would be easier to do the pcb's at home, if they are one side.

I think it can be one side anyway, I can put the ATmega32U4 on the bottom side :)
SMD stuff saves some space but not too much to make it worth it I think.
I expect the boards to turn out to be single sided with some jumper wires.


--- Quote from: hlavac on December 12, 2012, 04:00:53 pm ---

* Cheap to make
* Easy to make
* No FPGA / CPLD with hostile licensing policies
* USB connection, Full speed bulk mode transfer to enable fast programming. May use special driver or CDC serial port emulation or both. No HID (too slow)
--- End quote ---

you like contradictions don't you ?

its gonna be open source but use custom drivers ..
it needs to be cheap but were going to use a truckload of chips and boards.

and what's this hostile licencing policy on FPGA ? the software is gratis and you can use as you please.

I'd take an FTDI2232H ( note the extra 2 ni the part number ) , use one channel to load the FPGA from the PC so no programmer needed and use the other channel in bus emulation mode so i can send my data over. i'd wire up the io bank of the fpga going into the device pins to a programmable regulator. id use  an additional shifter like a max3373 to work anything from 1.2 to up to 5 volts i/o voltages.

Now, that was the easy part.

here is the hard bits that need solving before you begin this project :

- you need to make a list of chip pinouts indicating where the special pins are ( VPP ... 12 volt , 15 volt 21 volt -5 volt etc ... )
- where are you going to get the programming algorithms ?  programming a serial eprom over i2c or spi is easy .. real eproms a bit harder. flash eproms even harder and it will be real fun doing all the microprocessors.....

and as for cheap.... 250$ gets you a programmer that does all the stuff out there including JTAG ... that's gonna be hard to beat ...


--- Quote from: hlavac on December 12, 2012, 07:34:09 pm ---SMD stuff saves some space but not too much to make it worth it I think.

--- End quote ---


SMD saves a load of space, think about a simple resistor for example:
A regular 1/4W resistor can have a hole spacing of 10mm but in that space you fit 2x 1206 Resistors (and those are quite large), about 5-6x 0805's and who knows how many smaller ones.

1206 and 0805 are very much hand solder-able.

The space saved on IC's is pretty big too.


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