| Electronics > Beginners |
| Learning the Art of Electronics - keypad |
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| bd139:
Sounds good. I have a metric crap ton of LEDs and TTL ICs in stock so might be an excuse to use 'em all up too. I have three unfinished projects sitting around so I am going to resist for now :D |
| rstofer:
These days there is very little work being done with SSI or MSI (small/medium scale integration) so any chips I have can be devoted to this project and never missed. It will be good to use them up! It's going to be fun! |
| David1:
Got it! There's a schematic of the keypad in the old Student Manual (thank you bd139!) at the end of Chapter 15. Not sure what the dotted line on the right linking the square boxes means, nor the disembodied U4c bottom-centre, but it can't be that hard (famous last words!) |
| bd139:
Just a note the old student manual keypad is different to the new one. |
| rstofer:
Any way to post a decent image? I am thinking that building the keypad with an Arduino Nano and port expanders is the way to go unless a complete schematic can be found. Using a 3.3V Arduino with 3.3V IO expanders will work fine on the outputs to the counter. The logic levels on output pins will be high enough to work. All of the inputs (IIRC) are switch contacts so they won't be driving voltage to the Arduino. If there is a 5v logic input signal required, it will need to run through a voltage divider before hitting the Arduino. Not a big deal, just a couple of resistors. https://learn.sparkfun.com/tutorials/logic-levels There is also a lot of interest in using the 74HC595 shift register. This device can run on 3.3V (article below talks about 5V) so everything should work fine. The Arduino library has a ShiftOut function for driving the chip. Basically, you cascade as many devices as necessary (5?) and on every iteration, you shift all the bits (40?) bits. This needs to be done at a rate that works well for the keypad scan. I prefer the SPI port expanders because I can address individual chips. I can use just one 8 bit expander to scan the keypad, a 16 bit expander to drive the 7 segment displays and another 16 bit expander to send the address value to the counter. Simple and I don't have to drive the display or switch expanders until something changes on the keypad expander. 3.3V expanders are available in both 8 and 16 bits. https://www.arduino.cc/en/Tutorial/ShiftOut https://www.arduino.cc/en/Tutorial/ShiftIn https://www.arduino.cc/en/Reference/SPI |
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