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by stefanv
Fri Mar 10, 2017 5:00 pm
Forum: Wolfram Language
Topic: i dont see any point
Replies: 18
Views: 20213

Re: i dont see any point

stderr wrote:
curlyc wrote:i just dont see why this is a valid thing to learn
Big Maple fan?
If he were a big Maple fan, he would see the point. Mathematica wouldn't be his choice of product to use, but he would know its purpose.

Stefan (big Maple fan)
by stefanv
Sun Oct 23, 2016 12:52 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Issues found while scanning a matrix keyboard
Replies: 14
Views: 2437

Re: Issues found while scanning a matrix keyboard

Boy am I annoyed! The diodes in the keyboard are actually in the opposite direction of what is shown on the schematic. The reason my "diode alone" test worked was because I connected test leads directly to the diode, and of course I connected those the right way around, so of course it worked. Thank...
by stefanv
Sun Oct 23, 2016 12:42 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Issues found while scanning a matrix keyboard
Replies: 14
Views: 2437

Re: Issues found while scanning a matrix keyboard

Okay, I'm beginning to think you're right that there must be something wrong with my code. I've just tried a simple LED blinking program. When the LED is lit, there is 5mA passing through the LED (it's connected via a 270R resistor between a GPIO pin and ground). The output is 3.1V, which means that...
by stefanv
Sat Oct 22, 2016 11:18 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Issues found while scanning a matrix keyboard
Replies: 14
Views: 2437

Re: Issues found while scanning a matrix keyboard

I guess I should try measuring the voltage. I'll make a simplified version of my program that just does one row and one column and keeps the voltages static. Four diodes would have a drop of 2.4 to 2.8V, so even if the output was 3.3V, the result at the other end with a pull-down resistor would be 0...
by stefanv
Sat Oct 22, 2016 12:51 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Issues found while scanning a matrix keyboard
Replies: 14
Views: 2437

Re: Issues found while scanning a matrix keyboard

Well, my evidence that the software is working correctly is that it works when I manually touch a row to a column with a jumper. And, as I mentioned, when I switched to pull-low/read-0, it even works through a keyswitch or diode, but not both together.
by stefanv
Fri Oct 21, 2016 4:44 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Issues found while scanning a matrix keyboard
Replies: 14
Views: 2437

Re: Issues found while scanning a matrix keyboard

Makes sense. I wish they would just specify the no-load output levels, and the impedance, and we can take it from there to figure out the levels with particular loads.
by stefanv
Fri Oct 21, 2016 2:28 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Issues found while scanning a matrix keyboard
Replies: 14
Views: 2437

Re: Issues found while scanning a matrix keyboard

From GPIO-pads-control: To answer that question I/O ports have two parameters which deal with the output level:  VIL: The maximum low level voltage. (0.8V on the BCM2835)  VIH: The minimum high level voltage. (1.3V on the BCM2835) Can that be right? All the examples that light an LED using a high...
by stefanv
Thu Oct 20, 2016 1:42 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Issues found while scanning a matrix keyboard
Replies: 14
Views: 2437

Re: Issues found while scanning a matrix keyboard

They sound really horrible! Are they graphite pads? I believe they are something like that. The keyboard is out of a 1980s Yamaha organ. Given that the internal pull-downs and pull-ups are of the order of 50k, I wouldn't have expected 200R to make much difference. Neither would I have, and the 200R...
by stefanv
Thu Oct 20, 2016 2:10 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Issues found while scanning a matrix keyboard
Replies: 14
Views: 2437

Re: Issues found while scanning a matrix keyboard

Further findings: When using the reversed scheme described above, pulling the columns low and reading the rows looking for lows, the keyboard still does not work. However, the scheme does work when manually connecting one row to one column through a diode (this did not work with the original scheme)...
by stefanv
Wed Oct 19, 2016 1:18 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: Issues found while scanning a matrix keyboard
Replies: 14
Views: 2437

Issues found while scanning a matrix keyboard

First post here. I just wanted to share some findings while attempting to interface a diode-matrix keyboard to an RPi3. The keyboard in question has 10 "rows" of 7 "columns". Between each row and column is a SPST keyboard switch, and a 1N914 diode, forward biased when the row is positive wrt to the ...

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