Adrian’s electronics blog

I finally got round to finishing the improved version of my earlier pong clock which used two single colour 16×24 led modules with a built in controller. This version can display 3 colours and has several different modes to the earlier version and also it can display scrolling graphics from the popular retro game, pac-man. I’m calling this an arcade game clock as the main mode is pong and is inspired by old late 70’s and early 80’s arcade machine games. The case I originally was going to use got damaged but I’ve managed to put the prototype into an Ikea deep photo frame instead.

Now on to the electronics and in particular the LED modules I used. They are kind of standard but nothing like you would typically find on ebay however the firmware can be adapted to work with standard HUB75 1/8 scan modules. Unlike the modules used in the previous clock they do not have a built in controller and all multiplexing etc has to be done in software.

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I mentioned a while ago I had made a version of my single AA cell tester which can test high capacity LiFePO4 batteries with a nominal voltage of 24 volts (8 cells) which I had made for work as we supply 30 and 60 amp hour batteries which need to be tested. I have finally got the hardware and software version complete enough to a point where it works satisfactorily so I’m going to mention it here.

The basics

A simple battery tester that puts a load of approximately 5 amps or 10 amps (selectable) onto a battery with a typical capacity of 30 or 60Ah. The tester displays time lasted and an approximate total amp hour / capacity reading and prints the results onto a Epson TM88 series thermal printer. An RTC is included so testing time and date can be stamped onto the result then a receipt can be given to a customer if required etc.

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I’ve been making a timer for my garden watering system as I have bought a few cheap timers from Amazon / Ebay in the past but they were either rubbish or went faulty within a year so I decided to make my own. I used a 240×64 graphic LCD salvaged from an old & obsolete HP 9100C digital sender which I have had in my cupboard for around 14 years. It has a standard parallel interface so can be connected to an Arduino easily. The reason behind using such an over the top LCD for such a simple device was because around 13 years ago I intended to make a status monitor for my PC using LCDStudio software to drive it. The LCD was connected to the PC’s parallel port and housed in a project box containing the negative voltage generator (more on this later) and the backlight board. Anyway needless to say I got it to work; you can find some old photos of it in the project notes.

Like many things I never got round to actually using the status monitor partly because the LCDStudio software was not being actively developed and such didn’t work on newer operating systems. Also my new PC didn’t have legacy parallel ports and I could not get it to work with a USB to parallel converter nor a PCI-E parallel card. So it got forgotten about until I decided to see if I could get that screen working on an Arduino. To cut a long story short, I did and made a few test circuits including a text adventure game, serial terminal and a graphic LCD clock. I got bored of that adventure game and had no need for a 40 pixel wide serial terminal nor did I need another clock so I modified the clock into a water pump timer. The LCD screen uses up almost all of the pins on an Arduino Uno / Nano so it wasn’t much use to me for anything else. Said clock code came from a demo for the T6963C library which needed major modification to work on modern versions of the Arduino IDE as it was still using the .pde file extensions.

So on to further details about how I went about making it…

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If you have been reading my blog you will have noticed I made two Arduino based NIMH AA battery testers around 2 years ago. One was the first Arduino project I made but it needed some improvement and as I had mentioned in one of my previous posts I’m really running out of things to make; I don’t want to end up with a load of gadgets I’ll never use. So I decided to revisit some of my earlier projects and either scrap / repurpose them or improve them. The second tester I made does not really need further improvement as I have already done that and it only gets used once in a while. It is sufficient for my needs so I’m not that concerned about it’s shortcomings. This one however I have plans to turn it into a 12V lead acid battery tester but for now I decided to improve the display layout and make better use of the limited 16×2 LCD.

I had already changed the voltage reference from the inaccurate voltage divider method to a TL431 2.5V reference IC so in preparation for the conversion into a 12V SLA tester I have released an updated version of the NIMH tester code with the improved display layout I plan to use for the 12V version. The project page is here.

So next update I will probably show the completed 12V SLA battery tester although I have also been working on a 24V LiFePO4 version of it too which is complete and working but again needs further improvement. That will be shown in a future blog post when I feel the code is release ready. The pump control timer I mentioned before will get a full project page too when I get round to it. The priority now is to convert the AA tester into a 12V battery tester as I have a ton of them to test.

A while ago I made a rather silly project as I had a spare MQ2 sensor laying round left over from a previous experiment. I decided to build a circuit that simply displays the analog value from the sensor on a 7 segment display. It was a bit pointless but it did detect gas, farts 🙂 and smoke. I have since modified the project so it displays more meaningful results. I used an example to calculate the parts per million reading from the sensor by using a formula that works it out from the sensor’s response curve. This is found in the device’s data sheet. I still don’t expect it to be accurate but it definitely works.

I’m going to be re-visiting some of my earlier projects and either scrapping or improving them now that I have learnt more about embedded programming and Ansi C / C++.

The original post and modified code is here.

Just over 2 years ago I bought an Arduino Uno development board and began to see what I could do with it. I looked online for inspiration and came across this pong clock by Nick’s LED projects. I immediately thought now that’s cool and wanted to make one for myself and set about trying to source the parts. I had difficulty finding the LED panels used in Nick’s clock (I could only find the larger 5mm LED modules) and used ebay’s feature to email me if any of the ones I wanted became available.

I forgot about it for a while and in the meantime I made a few basic projects mainly based on someone else’s code and modified it accordingly then the email dropped in my mailbox that some of the 3mm LED matrixes were now available. I could only get red ones and they took a long time to arrive from China. I also ordered the case made from a jewelry box as suggested by Brett Oliver who is another maker who built Nick’s clock and made his own customisations to it. I don’t know why but I put those parts into a cupboard and forgot about them.

I came across them a month or two back and decided to put the clock together and make a few customisations which included changing some of the modes, adding PIR support so the display turns off when there’s no-one in the room and adding a separate 7 segment display which displays the time when the matrix is off and room temperature when matrix is on.

Anyway that’s the intro, let me show you a bit more about it:-

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