I have been playing around with driving 7 segment leds and have a good understanding of how it works. What my ultimate goal would be, is to read what segments are illuminated on an external 7 segment led in order to react to that information. I have setup a 7 segment led and am driving it from one Arduino - no problem. The issue that I am having is from the second Arduino, I can't seem to read the state of the pins via digitalRead/analogRead - is this possible? Am I only seeing issues because I am using two Arduinos to simulate the real problem? I have searched for some info and haven't found much.
Any advice would be appreciated!
thanks
Jsnmcdev...
Can't Arduino 1 send a message to Arduino 2, telling it what it is displaying? Trying to read all the pins seems like a really cumbersome and round about way to do that.
I am just trying to initially simulate the real problem. I have an existing piece of equipment that I am trying to get the data off of the led. The situation with the two Arduino's is just my test environment.
There are two chips near the LED. The larger one has no identification. On the back of the board it looks like a few of the traces run from this chip to the LED.
The smaller chip to the left is a atmlh340. Those are the only ICs in the vicinity.
My goal is to have the Arduino figure out the number on that LED and sync it back to a phone or another Arduino. From the phone I want to control that device, so I want the Arduino to basically "click" the push button until the LED shows the desired reading.
I then need to sync that value to another device - it is basically a video TX/RX that you have to manually set the frequency on both devices. I want to control this from a phone or from the RX ( where the TX would sync to the RX).
if you can tap the segment lines on the display and the ground line of the system driving the led (which it would seem that you can), then you can use drivers to isolate the segment signal from the #2 Arduino. May be opto isolators, ot high side switching?
123Splat:
if you can tap the segment lines on the display and the ground line of the system driving the led (which it would seem that you can), then you can use drivers to isolate the segment signal from the #2 Arduino. May be opto isolators, ot high side switching?
This is the problem I was considering. Tapping the voltage directly on the LEDs wouldn't give you logic levels, due to the LED voltage drops. So putting opto's in series would be another way. One of many, but it's a question of what's the easiest or most practical. If you can tap the IC before the current limiting resistors (assuming you can find them, and they're external to the driver IC), then you can read voltages. Another thing, you should really scope it to make sure it's not multiplexed. Even if it is only 8 segments (including decimal point). Or roll your eyes around and look for a dot trail, the caveman way.
Nice thing about the opto's would be that you wouldn't have to worry about ground loops.
aarg:
Tapping the voltage directly on the LEDs wouldn't give you logic levels, due to the LED voltage drops.
However an opto has a lower threshold than a red LED, so in parallel with the segment and with a series resistor you should be able to steal a fraction of a milliamp and sense the opto output using the internal pull-up of the Arduino.
Paul__B:
However an opto has a lower threshold than a red LED, so in parallel with the segment and with a series resistor you should be able to steal a fraction of a milliamp and sense the opto output using the internal pull-up of the Arduino.
True. I'm still trying to imagine what kind of equipment has one digit.
Thanks .. Tom...
The biggest problem you will have with the device you want to finally read the 7seg displays is that they will probably be multiplexed. What is the other device?
Thanks for all the information so far! I had no idea that this part of the project was going to be so difficult! I have been messing around in robotics and basic projects for the last 10 or so years, but have never tried to hack on existing hardware like this ( by trade I am a software engineer).
So the equipment that I am working on is the Boscam RC805. This is a simple 5.8Ghz video receiver with only 8 channels, hence the simple single LCD. This model has a big brother that has 32 channels and that was my long term goal. There is also the video transmitter that I will need to modify, but that one contains individual leds vs. a single segment. But first things first I guess.
I don't really have any information on the hardware other than what I can see. I don't have much code, as I have only setup a prototype 7 segment led, with an Uno. I figured out how to drive it, then I moved onto adding a second uno to read the values in - and that is where I got stuck.
The first 3 pins reading down from the upper left, on the module with the can shield on it, are almost certainly the binary select lines going into the 7 segment driver IC. So if you can read those, you only need to read 3 values, not 7.
