I have an older LCD Serial Backpack from Scott Edwards Electronics. It wants inverted serial signals, and the Arduino doesn't have the option to generate inverted signals with it's standard library.
I wired an inverter out of a quad NOR gate, but it's a 14 pin package, and you're supposed to tie all the unused inputs to ground. That makes for a lot of wiring just for a single inverter.
I've already got 3 BCD switches and an RGB LED wired to my breadboard and attached to my Arduino, so the breadboard is getting REALLY crowded.
I've seen notes out there that say you can use a low power NPN switching transistor and a couple of resistors to rig up a simple inverter circuit, but I couldn't get it to work.
Here's the link:
I tried using a couple of different resistor values: 100k for the input resistor and 10k for the supply resistor, and 10k/1k. Neither worked.
Can somebody recommend a simple inverter circuit that doesn't involve using a 14-pin DIP with connections on 12 of it's pins? That takes up a lot of space on my breadboard, and is a pain to wire. Supposedly single-inverter ICs can be had, but the only ones I could find are in surface mount packages. I couldn't find a DIP-4 or DIP-6 package.
I have a decent collection of PNP and NPN switching transistors lying around...
We need to know exactly what this backpack is and why it would not match with a library; if the perfectly correct inverter circuit you have tried does not work, it suggests there is a misunderstanding somewhere in the request.
First, did your LCD work properly this way?
If so, there may be two ways to fix it.
1- Some IC's have inverted outputs. Need spec's on the backpack.
2- Modify the library to invert the signal.
Paul__B:
It is not obvious what you are requiring.
We need to know exactly what this backpack is and why it would not match with a library; if the perfectly correct inverter circuit you have tried does not work, it suggests there is a misunderstanding somewhere in the request.
Please post a link to the backpack in question.
The backpack is an "LCD Serial Backpack" from Scott Edwards:
It's an older one (rev 3 or 3a, if I remember correctly.) It wants 5 volt serial input, but with the signal bits inverted.
I was able to get it working just fine using a quad NOR gate, but as I said, it's a 14 pin package where you have to tie all the unused inputs to ground so it takes up a lot of breadboard space and is a pain to use.
I finally figured out that the NPN transistor I had used non-standard positions for the collector, emitter, and base. Once I sorted that out I was able to build a simple transistor-based inverter that worked just fine.
I simply wired the base to my non-inverted input through a resistor, connected the emitter to ground, and wired the collector to my inverted output, along with a connection to the 5V supply through a pull-up resistor. When the input to the base is off, the transistor does not conduct from the collector to the emitter, so the output is pulled high by the pull-up resistor. When the input is on (+5 volts), current flows from the transistor's collector to the emitter and to ground, pulling the output to ground.
I don't have my notebook handy so I can't provide the resistor values.