When working with solderless breadboard, one of the concerns is how to power it. Ideally I would have a nice bench PSU but, being cheap, I makedo without one. In the past I have stumbled around with various solutions, including using the power pins on a USB serial breakout board, using an AVR programmer header just for the purpose of power, and my best solution so far: hacking the end off a USB cable and soldering some PCB pins to the power strands of the cable.
Using a 5V USB charger, such as the Apple iPad/iPhone device, is definitely a good starting point. These chargers are everywhere and can generally supply at least an Ampere, more then enough for my breadboard needs. The problem is attaching the “host” end to the breadboard. My solution is a simple one: a little PCB which contains a USB-B socket and some PCB header pins to connect the board to the breadboard.
For what it’s worth, here is the schematic:
And here is the equally trivial PCB design. I did not bother to align the silk-screen, since I only need the copper artwork:
I made 3 of the little boards, attached together until etching, after which they were scored and broken apart. One board section didn’t etch well, so was discarded. Of the remaining two, only one has been soldered up. Here it is attached to the breadboard:
It’s a nice little device, I think. The switch makes it easy to reset microcontrollers on the breadboard, etc. The purpose of the screw terminals is to tap out the power rails to another board or device, if desired.
The above picture shows some other progress. Last week I received the parts from UTSource: 3 FLEX10K (PDF) FPGAs and 3 EPC2 (PDF) configuration flashes. As I mentioned in my previous post, the first task was to check that I could program the flash with the Altera programmer. To do this required a PLCC20 to DIP adapter (bought from eBay), the flash IC, a 10 pin IDC breadboard adapter (made up a year or more ago), the Altera programmer, and a means to power the breadboard (described above).
Fortunately programming the flash worked without a hitch. I even created a JTAG chain, consisting of two flashes, and both (or either) can be programmed from the Altera software with ease. This was a big relief after the issues I had with the FLEX6000, though obviously this is only a small step.
The step after this was to draw up a schematic for the FLEX10K dev board. I have abandoned the idea of making up this circuit on my own PCB, and instead have gone for the breadboard approach, with the FPGA in PLCC84 being attached to the breadboard via an adapter. Here is the schematic for the dev board, as it currently stands:
Since the circuit will be made up on breadboard this schematic serves only as a guide when plugging everything in. The most important part is the linkage between the configuration flash and the FPGA. Note that this circuit shows the flash and the FPGA in a JTAG chain. I’m very keen to see how this will work in practise. Hopefully it will let me either program the flash (which will then send the configuration to the FPGA at power-on), or program the FPGA, in which case the configuration will only be implemented by the FPGA so long as it is powered. This will be useful in testing, since it should be a quicker way to see changes implemented in the FPGA, but in a final design is probably not that useful.
You can see there is no AVR this time. Instead an oscillator can is used to provide a test signal. I happen to have one laying around rated at 8MHz, so that will be the frequency input to one of the dedicated clockpins on the FPGA. This can then be divided down as desired. To test inputs and outputs, buttons and LEDs are also included. More complex stuff can be done via other ICs attached to the breadboard. One of my ideas is to use some seven segment displays to replicate the first programmable logic circuit I made on the XC9572 CPLD, that of the two hex digit up and down counter. Another thing I’m very keen to do is to see if I can attach the FPGA to my 6809 computer, since the eventual aim of all this is to include an FPGA (or two) as a critical part of my next 6809-based micro.
The next step, then, was to make up the PLCC84 to DIP84 adapter. This is a huge adapter, even bigger then the shrink DIP64 adapter I made up for the V9958. It requires 42 pins along the longer edge, almost the length of a breadboard slab. Here is the PCB design (a schematic is pointless here):
The width is the same as the shrink DIP64 adapter. You can see it provides barely enough room to route the traces to the PLCC84 adapter. I’m not currently able to finish this part, since I have no more PLCC84 sockets at the moment.
I was very pleased with the toner transfer of this adapter board:
And the etch went really well too:
After that it needed to be drilled out. I think I am very slowly getting the hang of drilling:
So I have to wait before continuing with the adapter build to receive the PLCC84 sockets. I have ordered 10, but since they are coming from China, I’m not expecting them for a few weeks.
In the meantime I will start on the VHDL coding for the test designs to run in the FPGA…