LED Matrix

As part of a project to find and organise small parts such as lego I’ve designed and built some RS485 addressable matrix displays.  These have a simple protocol to set an address (1 character) for each module and turn on one LED at a time in the matrix.   They are intended to be chained together.   There is a small step-down power supply on each board that drop the 12-24v power down to 5V using the LM2574 switching regulator.   Each board has a 4pin mini din connector which has the twisted pair signal, ground and power.



The project which will use these boards is a web application that can store where parts are stored in storage units.  The idea is that one LED in the matrix will light up to indicate the position of a part as you move through a pick list in the web app.  As only one LED lights up at a time it is possible to drive the single LED from the ATMega processor.

I originally wrote the server side project that stores where parts are in node.js, angular and MongoDB, however I have recently moved this to a Spring cloud application (mainly as a learning exercise).  The code is available at node or Spring.   The PCB layout was done in circuit maker and I will post it in a follow on post.   I am yet to check in the ATMega (Arduino) code but will package this up soon.

I’m currently updating all of this and also building some scales (connected on RS485) to weigh parts.   I’ll post an update in the next few weeks along with some instructions on how to get the code up and running.

Circuitmaker vs Eagle

I’ve been on the Circuitmaker beta since it went public and I’ve finally designed and order my first board.   The board is a RS485 addressable LED matrix (I’ll post some screenshots later).  I normally use Eagle for boards so there was a bit of a learning curve to get up and running with Circuitmaker.  In general I found Circuitmaker to be pretty good, however I’m likely to go back to Eagle for my next design.   Here are a few of the pros and cons:-


The 3D model was really useful for this design as it was a compact design were the matrix mounts on top.  The 3D model was great for checking clearences.  It also gives a slightly better indication of how difficult surface mount hand soldering will be.

While routing DRC are applied which allows you to easily and automatically avoid DRC issues.

Bigger boards than Eagle (free).


The component system can be slow and awkward to use.   All the components are looked up on Civa and have to be fully specced (i.e. values).  This is good if you wanted to produce a BOM that you can order directly from, however for the things I do I’de rather have configurable components which I can adjust and then manually enter the BOM with my supplier of choice.  You also need to have a network connection at all times.

In general I found it has a lot of spinners while you wait for network.  Even clicking a component on the schematic has a significant delay.

Windows only.  I’m normally a Mac user and I like being able to share my designs between my Mac an PC.

It has its own version control system.  As I like to store my designs on github which I can link too, the fact that Circuitmaker has its own internal eco system, which doesn’t seem to be easy to share outside Circuitmaker, is not ideal.  Some users have expressed issues with not having closed designs.  Personally I don’t think this is a problem as all my designs tend to be open.

Gerber export was tricky as it doesn’t output a board outline by default.  You have to add a keep out layer for the board shape.


I think if Circuitmaker was a little less sluggish and maybe had a better component system  it would be preferable to Eagle in a lot of cases for me so I’ll be looking at future updates to see if the situation improves, however for the time being though I’m going to go back to Eagle.

Ethernet motor control board

I’ve got a prototype motor control board up and running.   The board has 4 motor channels and is based on the ATMega and ENC28J60 Ethernet controller.  It has 2 through hole mounted H-bridges to control the motors.   The schematics are available on github and some example code will be there shortly.

I’ve done some testing on channel one and it seems to be all working correctly.   I’ve built a simple test UDP server using the Arduino libraries and this is all working correctly so far.   The only issue is that the original design did not use the PWM pins for the enable lines so there will need to be some bit banging for speed control.   I intend to update the design in the future to enable this.

A few pictures:-

Motor controller assembled

Motor controller assembled

Testing the motor controller

Testing the motor controller

These will eventually make it into the underwater ROV.   The idea was to control over ethernet and send video back over ethernet using a cheap IP camera.


I have received the latest revisions of a few boards I recently ordered.  I assembled the the newest Gardenstation board and there was an issue with shift registers (MR was being held low).   Some board hacks got it working and I’ve fixed the Eagle file and switched the display header pins around (will update in github shortly).

I’ve assembled on ROV control board although at present I’m not able to burn the bootloader on the AVR.   I suspect there is some issues with the soldering of the ENC ethernet controller.   Elecrow removed the solder mask between the ENC chip pins which made it extremely hard to hand solder.

I’ve embarked upon a reflow oven project (based on a Kmart $35 toaster oven).   I had a quick test at the weekend and managed to successfully reflow some parts to a test board.   The thermocouple I’m using has been slow to respond (my voltmeter one is much quicker) so it got a bit too hot.   The Arduino control code is available here https://github.com/markpudd/reflow_oven.

Quick Update

This is a quick update as the blog hasn’t been updated in a while.   I’ve been traveling so haven’t had a lot of time to post.   The arcade machine is finished bar the marque at the top of the cabinet and I will try an post some photos next week. I’ve made some minor changes to the Garden Station in order to add a power light and fix a few minor issues in time for the Australian spring/summer!  I order new PCBs from http://www.elecrow.com which I received last week however I’m currently in the US so won’t be able to assemble until next week. Finally I designed a small board to provide AVR with Ethernet and an H-bridge to use in a ROV project I’ve started to build.   The board parts have all been received and are waiting for me when I return home next week.   The design is on github – https://github.com/markpudd/rov_control.   I’ll probably hand solder the first one but I’m thinking of making reflow oven for future projects.

Raspberry Pi Arcade

I been considering build an table top arcade cabinet for a while.   Since I’ve had some spare time lately I decided to start a project to build one.  I wanted to use as much stuff that I had around to keep the cost down so I decided to use a Raspberry Pi for running Mame, an old VGA monitor, some spare particle board and an old ATX power supply.  I’m also keen to have the potential to change to a JAMMA board or old PC in the future.

For the cabinet I looked at a few internet designs (weeCade and some others) but decided in the end to just create a rough sketch in 123D and build based around the size of the monitor I had.


The next thing to do was to order in some arcade controls.   I used http://www.austinamusements.com.au and ordered their $30 bundle and a $17 coin mech.  I fitted a one player control board to just get things up and running.   I also needed to get a HDMI/VGA converter which came from ebay.   For audio I’ve used a cheap 1W amplifier kit and two 1W speakers.  


Time to wire the Pi up with the monitor and audio and have a quick test.   For the test I have not wired up the control surface so wss using a keyboard.   The Cameleon Pi distro has Mame installed so it was pretty easy to get up and running.   I had to changed the HDMI mode to 2 in the /boot/config.txt which fixed the audio out (from the HDMI adaptor) and as I was change the config I also increased the over clock to 1Ghz.   At this point everything seems to be working apart from the controls!ImageImage


The test control surface is built but not interfaced to the Pi.  I’ve had a few ideas on ways to do this:-

  • Buy a USB keyboard control surface interface.   There is some boards available for this purpose or the other option was to try and make one from an old donor keyboard.  I don’t have a donor keyboard and I didn’t want to buy the convertor.
  • Interface the controls directly to the GPIO on the PI.   This was my original though cut to it being reasonably simple however there is a limited number of pins.  For a 2 player, 3 Button controller with P1/P2 buttons and coin mech I’de need 17 inputs.
  • Using an IO expander IC on SPI.  This wasn’t a bad idea but I need to order in some expander IC’s…
  • Use an Arduino to control get the inputs and convert to SPI.  This is option I’m going to go with as I have all the parts.   I am short one input as I am using an UNO so will put the coin mech either on a Pi GPIO or make it use the same as P1/P2 pressed together which would also allow adding credits without using coins an alternative would be to use multiple inputs on one analogue input using a resistor network.  Using the Arduino also has the advantage of allowing extra features easily (such as auto fire) and has analogue inputs if required.

As I chosen to run with the Arduino solution I’m currently doing a little research on how to get SPI working between Pi/Arduino which I’ll post on once working!

I’m also looking to get a backing printed for the control surface which I will then cover with some clear plastic sheet.



Car Lights

Got a kids ride-in car with no lights or battery indicator?   If so this is the project for you.

The goal of this project was to create a simple microcontroller board that will control  some indicator lights, hazard lights and battery monitor for the kids ride on car below.

Kids car

Kids car


The project uses an ATTiny84 micro controller to control all the lights an monitor the battery level.  This can be build on a simple piece of stripboard.  Here is the original circuit diagram and stripboard layout. There was a couple of minor change in the final version which we’ll discuss later.


Firtzing was used to create the circuit and stripboard layout.  The circuit diagram was created first which caused some issues when trying to layout the stripboard.


The build was started with a breadboard layout of the LEDs and a potentioner to simulate the battery level.


This was connected to a standard Arduino UNO board in order to write the firmware for the ATTiny.  The firmware  (and circuits) are available from github (https://github.com/markmoro/carelec).   The firmware is super simple as its basically blinking some lights so it should be easy for anyone to follow and makes a great introduction to Arduino coding.

Once the firmware was complete it was time to build the ATTiny version.   The first thing to do was to write the firmware to the ATTiny.   To do this we used the Arduino as an ISP.  There is an excellent tutorial on instructables on how to do this here.  There were some issues with pin mapping with the Arduino pin numbers.  The actual pin numbers are shown in the diagram below:-

ATTiny84 Arduino Pin map

ATTiny84 Arduino Pin map


Once the stripboard layout was built and the ATTiny programmed the the build into the car can be done.

Circuit on Board

Circuit on Board

We soldered the LEDs on to wires and ran them back to the main board were we had header connectors to plug the in to the board.   The following section were made:-

  • Left Indictor
  • Right Indicator
  • Hazard Lights
  • Battery indicator lights
  • Switches

We’ve simply taped all the wire runs in the short term but will probably secure them up more in the future.


The majority of this build went pretty smoothly, however there were a couple of issues.

The first issue was that when plugged into the main car battery the ATTiny kept reseting.  We had previously tested using a 8 AA cell battery back so the power was the main suspect.  A small value capacitor was placed across the ATTiny’s power and this solved the issue.  Its important to note this need so be as close to the ATTinys power pins as possible.

The second issue we had was wiring the power on/off to the cars on/off button.  The cars on off button seem to have so strange ground wiring (I assume this is for the motor to run back and forward) and it turned out we couldn’t wire the circuit on/off to this.   As a simple solution a second switch was added.  The main switch could be replaced with a dual-pole version however we will probably not do this.