Hum a (oscillo)scope... Since you like building strange (and real cool btw) stuff, you might get tempted by the dark side of electronics...
Thanks! And I will keep that in mind. I remember seeing one at a science exhibit as a kid and loving the effect. In the meantime, if you think it would help with the build I might see if I can track down someone nearby that has one.
I was wrong about pin 8 in my earlier post (no need to solder anything there, very sorry!). It is pin 10 that is the TXD that we need. This should thus be "high" almost 100% of the time. (Until we start sending commands to the tablet, something that almost never occur during normal operation -- only when the "driver" initializes to query the tablet).
Oh good, I was worried about having to solder something so small! And yes, pin 10 reads high the whole time, at least during the operations I was performing.
First you gonna need to make sure the Teensy you got works. That made me think : You have a spare mini-usb cable
, don't you? You are gonna need this. So first thing is to plug it in naked and see its led blink. Next step (unplug it) is to solder the 3.3v regulator (there is a trace to cut and a solder-jumper to do I believe -- follow the instructions from http://www.pjrc.com/teensy/3volt.html
). When all done, replug the Teensy should still blink. Use your multimeter and with the black on a GND pin, probe the voltages, you should be able to get 3.3v on the VCC pin(s) (there are two of those, pick the pins away from the connector, it is more convenient). There is enough Amps left to power your digitizer from this 3.3v output.
Great pictorial! Looks simple enough.
It is always a bit tricky to know which is which when connecting TXD and RXD. Labels for UARTS are always a mess. You have to know the "direction". Look at our wiki to see the direction (tablet --> host or tablet <-- host) and from the Teensy side, "TXD" or "TD" means "Transmit Data" and "RXD" or "RD" means "Receive Data".
But because we see highs and lows on pin 9 with pen activity, this is most likely RXD because this pin is sending data out to the computer, right?
Oh yes, it looks like you are working with a whole different beast there but it helps me understand what the different pins are doing on both Teensy and the tablet.
BTW, when you are done, it would be nice to have a connection summary with a couple of pictures of the finished stuff to help out the next folks that want to do this.
I will supply you guys with everything I have. Even though my digitizer is not the same as others, just the fact that people were doing this with others is what got me to take up the challenge (and for me, this is a challenge). This place is great and I'd love to contribute.
If these are the micro-coaxial types you are not going to be able to do anything with them. We tried hard. Try to skin and solder onto the ones that are not connected before cutting the other ones. You'll see immediately if it works on not. (use your multimeter to check the continuity).
Never heard of these before, but it got me worried enough to test it. I cut off a segment from one of the unused lines and soldered the ends to another wire. We are good to go.
BTW, your multimeter is analog right? (with a needle): Does it have the continuity test (often with a beep for the digital ones, but it would work with a "OhmMeter" function too). If unsure, attach a picture (or a link to a picture of a similar model), detailed enough so I can read the letters.
I think? It's the thing I use to test for a closed circuit, right? This is mine right here.
Also can it measure Amps?
I believe so. It has a DmA setting.
To measure Amps, you have to connect the leads "in serial" (like the power must go "through" the multimeter).
So while experimenting, it would probably be best to use some sort of connector instead of soldering the lines directly to the board, that way I can move things around and splice in the multimeter easily. Do I need a multimeter for each of the four wires to watch for spikes or do I only need it on one wire?
Pin 14 looks like a ground -- but because the DGND is connected to it -- it might be why it is not connected -- From what I can gather, DGND is a "Digital Ground" and is typically more "noisy" than a AGND (Analog) -- or plain GND. The ground must be going elsewhere. I see "AGND" on the board. Check on which pin it is connected to..... .....For connecting to the Teensy GND, both will most likely work, I think I prefer AGND, but anything that would already have a connection through the cable is much more convenient of course. -- I think AGND is normally Pin 1, right?
I just tested it and the results are that both pin 1 and pin 14 are connected to AGND and DGND, which I guess would also mean AGND and DGND are connected. I scanned the board looking for another pad but I am not seeing a plain GND.
Pin 11 and 12 always been quite mysterious and contradictory. From your readings, it seems there is only 1 pin that is connected that stays low all the time (pin 11)
That is correct, I didn't get any readings on it at all.
why did you put the letter "G" for pin 1 and 14? You meant "Ground" I suppose(?).
Yes, G meant that it was connected to the DGND pad (and now we know, the AGND pad as well).
In the laptop, was there anything else connected to either digitizer boards that would ground them?
Hrmmm, there are these pads were the screws go on the connector that plugs into the motherboard. I can get a connection between them and the GND pads.
I played around with it a little more and I know pin 1 and 14 make contact with the silver housing the connector slides into. That conductive fabric is attached to the housing, so I initially thought this was how the ground was transferred, so to test this I pealed it back so it no longer touches the metal at all, yet I still get a connection between this housing and the end of the cord (where it connects to the laptop). So now, really, I have no idea how the connection is extending the length of the cable. Maybe once I strip the wires something will start to make sense. What do you think?
Thanks for the help, I will follow the Teensy instructions when it gets here.