I have had a kit for building an i2c sensor for the Mindstorms NXT for many years, and done nothing with it, other than losing one or two of the components (easily replaced). It requires soldering and I have hardly done any soldering since I was a kid. Now that I have developed some electronic skills, I thought it was time to try some soldering, so that I can buy kits that require soldering. The emonTx from OpenEnergyMonitor is one such kit that I would like to buy as it uses a lot less power than my current energy monitor, and could also be used as a room sensor, with a little modification.
I thought I would use the PCF8574 to control my button pusher from the NXT. By combining a couple of projects from Extreme NXT, I can use the PCF8574 to drive up to 8 simple MOFSet amplifiers to press buttons using solenoids. I bought a couple of cheap solenoids off ebay, and they seem to do the job.
I will be able to push several buttons simultaneously, so I could play chords on a keyboard, as well as drive equipment that needs button pushing. Sending a byte via i2c to the device will define the up/down position of the 8 buttons.
I plan to put the button pusher in a box with a NXT socket for control and a power jack socket for a 12v power supply. it will also have a strip connector for connecting the solenoids. It will be easy to control this from an Arduino rather than a NXT using a chopped up NXT cable. This seems quite a good way to package my button pusher. The arrrangement of the solenoids will depend on what is being pushed or played, and that needs a bit of Lego or some other construction.
UPDATE: I have successfully built this. My soldering wasn’t too bad. However, the Mofset part of the circuit is still on a separate mini breadboard. Transferring it to the mindsensors PCB looks quite a bit of work. I am still not sure about the best way to package this.