Picture of LED Microcontroller Debug Module
PIC Debug Module-6-2.jpg
PIC Debug Module-9-2.jpg

When it comes to debugging a microcontroller circuit, there aren't a lot of simple options.  Since a microcontroller circuit might have multiple things going on at the same time, measuring voltages with a DMM isn't an option.  Using an computerized In-Circuit-Debugger solution is expensive and elaborate, and time-consuming to set up.   People often resort to connecting banks of LEDs to the circuit, but this also takes time and if wired incorrectly, might mislead you about the issues you are trying to solve.

Enter the Microcontroller Debug Module (MDM).  It is a device which simply transplants the microcontroller (MCU) to a separate unit, away from the breadboard.  It is connected by a 40-pin ribbon cable to a small PCB which takes the place of the MCU on the breadboard, transposing each pin directly.  No circuit modifications are required for the operation of the MDM.  On the module are 74LS541 8-bit Line Driver ICs which drives indicator LEDs for each of the 8 bits on each of the data ports on the MCU.  This chip delivers current for the LEDs without affecting the pin of the MCU itself.  The pin and the breadboard circuit have no idea the chip is there.

My microcontrollers of choice are PIC18 family 28 and 40 pin PICs which I have designed this unit to be pin-compatible for.  Your unit can be designed for Arduino Atmel chips or any MCU you wish to use.  

This Instructable is mostly intended to inspire ideas and some circuit pieces to help you develop a MDM for your own favorite family of MCU.  

Also Please note the schematic and board layout are regarding Revision 0.3, it is far more advanced and has numerous corrections/features added to it, compared to Rev 0.1, which is photographed.
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klee27x3 years ago
"I am always open to suggestions about how to make this better, or what other features it could benefit from."

I could suggest a few from my DIY 8 channel logic probes:

Some of the features that you might want to consider adding:
1.True logic probe - high Z = both LEDs off, for differentiating between high impedance input and rapid switching outputs
2. individually selectable pullup/down resistors. Handy for quickly differentiating between an input with pullup enabled and an output high. Also takes the place of a dev board in some cases.
3. Input capability: tactile switch on each line that is individually selectable to short to either the ground or the power rail
4. One one of them I've added a li ion battery with 5V DC step up converter for powering the probe and/or the target circuit
5. integrated 9 pin port for plugging an 8 channel logic analyzer.

Oh, and you got it backwards. Red = high, green = low, dude. :) Think traffic signal. Think ground wires are green. Think red/black wires, where red = positive. :) 

mattthegamer463 (author)  klee27x3 years ago
I was more thinking Green = good, Red = bad.

You've made some nice suggestions but unfortunately they're sort of "pie in the sky" ideas. I hunted high and low for an IC that would do the tri-state outputting like you say for #1, but I couldn't find any. This is the best I got. I'd need a different LED hookup scheme too, since a high-Z pin would result in both LEDs turning on anyway.

I'm not entirely sure what you mean about #2. That is to say I don't understand the value. If you've got a pulled-up input, you should be pulling it up somewhere in your circuit. This device is not to be replacing a circuit, just the PIC, also you wouldn't want to forget a key component in your design and have it fail after you make a PCB without all your pull-up resistors :(. That wouldn't be fun.

Same for #3 as #2.

However now a battery is a great idea. I will look into how cheaply I can achieve that, however powering by the circuit itself is almost always available.

Logic analyzer ports could be interesting. I imagine it is something that could be at least available on the board, even if there weren't soldered pins for it. I'll take a look into that.

Thanks for the ideas. Glad you liked my work.
This seems great when you think some pins are either misconfigured or internally damaged
mattthegamer463 (author)  frank260801153 years ago
It would be great for that purpose, as a PIC testing jig. I never thought of that. Glad you like it.
Elipsit3 years ago
Well done Matt, raising the bar yet again!
colin3533 years ago
I have never been so amazed, good job.