In preparation for installing a heated print bed and just to clean up from some previous mistakes, I cleaned up my print bed yesterday. I sanded it with several different wet/dry sand papers, washed it with soap, applied a metal polish and then cleaned with acetone. I only did this to the top since it is where the glass will lay and the bottom won’t be seen often anyway. Having it so smooth will allow better heat transfer from my aluminum sub-bed to the glass on top. The aluminum will be used to distribute the heat from the nichrome square wave pattern under it so that by the time it gets to the glass it won’t cause tension, cracking and shattering. I’ve had enough of that already, thanks. I was running a pared down clothes iron as a bed heat source before but that was dangerous, heavy, heated too unevenly, ugly, hard to control, had to be turned off manually and dangerous. Safety is worth mentioning twice. The plan now is to do from lowest layer up, a foam thermal barrier, nichrome square wave heat element secured with kapton tape, aluminum plate and thermistor, glass and then possibly some kapton to print on if I’m not getting good results from printing directly on the glass.
I took a break from my 9 to 5 (see SquidTooth.com) this weekend and made some progress on my yet to be officially named car door unlocking with my phone project. I got my phone talking to my Arduino via Bluetooth and my Arduino doin’ stuff based on that input.
I became aware of some limitations to the systems I was using that forced me to re-engineer my approach a couple times. The BlueSMiRF Gold board I was using for the Arduino side of the Bluetooth connection doesn’t tell the Arduino when it’s connected. Nifty that it just functions like a serial connection with no config required, though. Well, thought I, I could just connect and send something over serial Bluetooth connection from my Android phone (HTC G2). I went about trying to have a broadcast receiver run when the device’s screen was turned on so all I’d have to do is tap the power button on my phone. That way I wouldn’t even have to remove it from my pocket. The bad news is that Android doesn’t handle that broadcast the way one might think it would. The Android Team decided that it would take measures to limit what apps would run at specific performance critical points of device usage, such as turning the device’s screen on. There is a way to get code to run when the screen is turned on but it basically involves always running and telling Android that is what you’re waiting for. Not ideal. So, I adjusted my design again.
The idea now is to tap an icon on my screen that connects to the Bluetooth in my car which unlocks the door. The Arduino will then send back confirmation that it was successful and the app will close and display success. I got most of that working. I seem to be having some issues with reading the message the Arduino sends back from withing the Android code and I’ve yet to actually do any door unlocking. I still need to order those actuators and install this all in my ride. One other thing I’m not certain about is connecting the Arduino Pro Mini I have directly to the car’s power. A fully charged car battery can put out more than 12v which is the Pro Mini’s stated max voltage and then there’s also the issue of the voltage that the alternator supplies. I may have to get a voltage regulator to go before my Arduino’s built in voltage regulator. I’ll post stuff as I figure it out and code will be up as soon as I have a few more things finalized with it.