Time for some pictures.Remember that I did have this all setup and working and I just don't have any pictures of that. One of the items I wanted was buttons for user input but I didn't want them built onto the display so I found this awesome remote on Adafruit that had a momentary receiver that it worked with. It also has a latching and toggle.
Most of you reading probably know that the raspi is 3v but this remote put off 5 volt signals. So I made a simple voltage divider circuit for each output. I think I used 2200 ohm and 3200 ohm resistors (they were what I had lying around) As you can see I covered the back in hot glue to make sure nothing short circuited. I also had a ribbon cable come off the board instead of the standard header.
The next step was to setup the monitor so I could use a digital pin on the raspi to turn the screen on and off. This was a simple npn transistor setup.The emitter is on the ground side of the button, the collector is on the 5v side and the base goes to to digital output. Make sure you have a resistor inline from the digital output or you are basically connecting your positive voltage directly to ground. The picture below is a little hard to see but at the right of the image you can see the transistor hot glued directly to the pcb. The resistor is in the heat shrink tubing on the top of the pcb and you can just see the white wire on the far right.
Since my monitor has an external power brick that feeds 14v into the monitor it was easy to get a dc-dc converter to make 5v output for the raspi and rf receiver. I decided to mount the converter inside the back panel with the pcbs from the monitor. There was a nice little space where I could bolt the board to the frame. I used an abs spacer from a screwed up 3d print to keep the board from short circuiting. I would have designed and printed a special holder but my 3d printer is currently broken. (a stepper motor shaft sheared off) I know I should have used different color wire for the positive and negative wires but red is what I had. The easiest place to connect the converter is directly to the barrel plug pins. The right picture is the back side of the metal enclosure. If you look closely you can see where I relocated the monitor buttons to. You can also see my 5 volt line coming out of the metal enclosure. Since I needed a signal wire, hot and cold I used a standard servo extension wire that I had lying around. This way I can easily disconnect everything from the monitor if necessary. I like to build connectors in when possible just in case something happens.
Next was mounting the raspi. Again I planned to print a nice mounting board but since I was on a roll I decided that I could reuse a miss print. To mount the board to the holder I drilled slight small holes and used metal screws to add threads to the holes. I used nylon screws to hold the board to the holder just because that is what I had lying around. To attach the holder to the metal enclosure I had to bend a piece to the holder up. Since 3d printers use thermoplastic (plastic that when heated above a certain temperature becomes pliable and when it cools it hardens again) I heated up a piece with a heat gun and bent it up 90 degrees. That lined up with a hole already in the metal enclosure. I had to drill a hole in the enclosure to secured the holder to the enclosure better. Below you can see things starting to come together.
Next I need to mount my rf receiver, and make my connections between my raspi, the rf receiver and the power transistor. In theory the only other thing to do is make a nice frame and the project should be done, but we all know it is not that easy. I plan on making a new sd card with only the required software on it instead of having all the extra stuff from when I was trying to get everything working.
Wich npn transistor did you use?
ReplyDeleteIt was whatever I had lying around in my parts bin. It was probably either a 2n2222 or a 2n3904
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