Following on from my previous post on my DIY timer I wanted to make something that I could mount to the wall and not have my wife be ashamed of it! In passing on one of the car forums I frequent I said that I could modify my original heating timer to be controlled by a google calendar for less than €100. As you know that timer died while experimenting so i was left having to make one from scratch if i was to come good on my claim. Thinking about it an arduino combined with an ethernet shield and touchscreen shield could come together to make a very nice controller with a tidy looking interface. The hardware for that should come in under €100. 20 each for the shields and arduino and a further 10 for a solid state relay. It was while browsing DX.com i came across this. A 4.3″ touchscreen android tablet for less than 35 euro delivered – mind blown, I knew what i had to do.
Hardware wise I needed a way of allowing the tablet to turn on the relay. I couldn’t use bluetooth as the tablet didn’t have it and it would be too unreliable anyway. The next choice for getting an output would be the vibration motor but again, the tablet didn’t have one. All that i was left with was using the speaker output to trigger the heater. To do this i had the software (detailed later) output two tones. Depending on the frequency of this tone we would know if the heating should be on or off. The speaker output is passed into an op-amp used as a comparator to give a nice 5v square wave that is input into an Attiny85 via one of the Boards.ie keyrings/dev boards i had made up. The attiny measures the incoming pulse and decides whether to turn the output on or not. The solid state relay can be directly controlled with an attiny pin. Here you can see the hardware during the prototype stage.
Following on from the first post where the voltage was dropping when the motors were under load causing the arduino to reset i tried a couple of things to get around the problem, first i added another cap across the arduino supply and then i added another battery in series (to give 6V total) but still the voltage was dropping too much.
As i knew running an arduino from 4.5V was on the low side i went looking for a dc-dc boost to up the voltage to something more useful. What i found was a module used for charging USB devices from voltages down as far as 3V. These are rated at 700mA so more than enough for what we’re running off them. The actual output voltage is 5.5V which is in the acceptable range for the arduino.
With the Dublin Mini Maker Faire just around the corner i treated myself to a new toy to hack in its honour, yeah i know, any excuse. Everytime i look at my 1:18 scale delta integrale (a reminder of the one i used to own thats sorely missed!) i always think that it would make a great project to add working lights to it and have them controllable. Then i remember how much the model cost and i decide not to chop it up, not yet anyway. As i was browsing the argos site to look for anything interesting and cheap i came across this Porsche 911 GT3 RS which seemed like a nice buy.
Our TV is controllable over wifi from an android app and this has proved very useful as i’m rarely seen without my phone either in my hand or at least in my pocket. The TV remote (a Harmony One universal) has a habit of hiding down the side of the couch and generally going missing. The number one use for the TV is with the Sky HD satellite box and not being able to control it from the phone was definitely inconvenient (#firstworldproblems) and it’s something i wanted to remedy for quite a while and its something i started looking at a while back.