PI/Arduino Processor Emulator

Despite being pretty hectic with work, I have now added another feature to it which mainly was for my benefit but has proved to be a useful add on.

One problem ive had over time is how to tell if a TTL logic chip is working properly or not. Sure it can be tester by logic probes or scopes but ultimately the device is removed and another fitted, often with no real change to the board. Stuck pins are common and sometimes inputs cause issues.  Anyone that debugs boards will know this. Piggy backing sometimes works but it can be a slow process.

This tester apart from everything else it does, will now test most TTL devices on the board while the board is powered up and running. It wont affect the boards operation but will clearly show whether the device passes the truth tables or not. If it fails, a little work is needed in checking the results but if they look ok, then the tester can learn and then get better next time. It will also check for stuck pins and show tied ground pins or pullups.

All data is stored in files which can be backed up on usb sticks etc.

Ive added a few pictures showing the screen shots of it in action.

Test clip over a chip. The clip is a 20way which covers most TTL devices. 

Testing a 74LS00 while the board is powered up and running the game. This one passed the tables

Front of the tester showing the Active Device Test screen. Ive called it this as needed to think of something lol.

So far, the tester will now do the following:

1) Actively test most TTL devices on the PCB without affecting the game running. Clocks may be slightly bothered due to the additional cabling.

2) Simulate a Z80 or 8080 processor allowing full data and address control. More can be added as software is improved.

3) When using the processor connection in 2 above, ROMS can be read and dumped into BIN files.

4) Memory maps can be interrogated allowing vital select lines to be toggled. 

5)  Some RAMs can be written to and read.

6) I/O ports can be checked.

7) Audio signals can be traced using the probe.

8) Built in logic probe clearly showing the state and duty cycle of any pin.

9) Test programs can be generated using a known good board and then applied to faulty ones. Helps identify faults quicker.

Future improvements will include a 2716 and 2708 eprom programmer plus more things as I think of them.

This has developed due to my need to debug Space Invaders etc and has so far helped fix three boards. It is intended to be a stand alone unit which without much technical knowledge allows someone to trace faults. No scope etc is needed but obviously it should be regarded as a tool and hence schematics and some level of skill is needed to take the information it gives and apply it to tracing the faults. Its an ongoing project so improvements are happening all the time.

Depending on the interest this gives, I will be looking to make these to order. The unit will include a Pi3, Arduino, LCD touch screen, and IC tester pod. A manual will also be included and details on all the front connections so the processor connections can be easily made. Aiming to use a two sided PCB as the unit I have is wired manually and a mess tbh. Estimated cost atm is £350.

Cheers

Mark

1) Can an external display be added. 

The unit runs under Linux and is using a Pi3 to do the user stuff. As a result of this there is an hdmi connector and switching between the LCD and hdmi is simple. Instuctions will be given on this.

Note that as its a Pi3, wifi and bluetooth are built in so full internet access is available plus all the usual Pi features. The tester is a app thats simply run.

2) Does it give live updates on logic pins.

The answer is yes. The A.D.T , or Active Device Testing takes effectively a snapshot of the chip under test and graphically displays them. Stored truth tables are then applied to determine if it passes or fails. Stuck pins are detected by change of state. Pins tied to ground or 5V clearly will show as their state but pins which should change and dont will be shown too.

Also i forgot to add before that theres also a basic voltmeter which is enabled when the probe is switched to audio. Nothing major but it will measure most supplies DC on the board.

I echo the sentiment of TheGecko

In theory this should be able to be programmed to test LS244/245/373 etc in circuit.

I hate the idea of compile-in for this kind of thing, are device definitions going to be in some folder somewhere so we can all contribute?

That would open the floodgates for 2114 (already does this I know), 5101, 2148, 6116, 6264 etc

Just give us a big enough clip lead and we're sorted.