Hello, this is my first little instructable.
I am a big fan of taking electronic things apart and look inside. I've learned much stuff about designs, chips and also salvaging parts out of old electronics is a cheap and easy way to get electronic parts for the next project. Also it is very interesting to have whole modules from stuff that got ripped apart or stop working. In this little instructable i will show you how i reused a "human machine interface" from a old tv receiver. It is a nice little module with a 4 digit 7 segment display, a green and a red led, 3 keys and also a integrated ir receiver for the remote. Everything you need for the next robot, arduino project or just learning stuff. So lets begin!
Step 1: Look What I Found: a PT6964, What Is That?
First take a look at the module and find out which is the main function of the module. In this case this was easy, there is a single chip a PT6964. Sometimes it is difficult to get a datasheet from the mighty internet, but this time it was the first hit on google.
In the datasheet you find a application example, most designs are easily using this. We see a serial interface to a microcontroller to send commands and data to the controller. We also see that the PT6964 can handle 7 segment digits and also read keys. Nice thing found in the trash can. So it seems the LEDs and keys are also connected to the PT6964.
Step 2: Connection
So we already have a idea how this module is working. The main part is the PT6964, let's see further. There is no microcontroller on the board, so the interface must be on the connector.
All you need to do now is take your multimeter an measure the ohms (or beep) of the corresponding pins of the PT6964 for the serial interface. The signals DIO, CLK and STB should be on the connecter 1:1 straight. Sometimes there is a resistor in the signal line to make the design short circuit proof, then you don't measure 0 ohms (or beep) but a couple of ohms (let's say everything <1000ohms is suspicious). In this case there was series resistors in the signal path. I found all signals on the connector. GND and VCC the same. First i could not find Vcc on the connector, because there is a protection diode 1N4148 in the Vcc track.
At least one signal on the connector didn't match to the PT6964, you can guess: the ir sensor signals. This one is not handled by the PT6964 and so the microcontroller on the old mainboard got this signal too. I noted it but i am not using this in this instructable.
Step 3: Now It Is Our Turn! Bring Me the Solder..
So we have the connection. Now i soldered a tiny little PCB with a Attiny2313 to give it a try to bring life back in the module. You can use a arduino or maybe a raspberry pi to connect the display too (maybe a made this for my 3d printer.. let's see :-) )
The datasheet contains all information to get the simple serial interface done. I used bitbanging to make it more portable to later projects.
The PT6964 is a amazing chip with a lot of nice features:
- dimming function using settings in the chip to adjust the brightness, neat!
- whole display on/off with one single command, save power!
- read keys and debounce them, just what you need to make a nice interface!
After getting the first life sign of the display i discovered that the segment connection is not as mentioned in the datasheet of the PT6964. I guess the designer liked to have a cheap single side pcb so they connected everything as it was the best from the point of view of the layout. But no problem a little try and error and you get the right segments. I created a little LUT (Look Up Table) in my code to get the right bitcode for every digit.
I host the code on github (i wrote this in one evening, don't be rude :-))
Step 4: That's It
So now i have a fully function 4 digit 7 segment display with leds, keys and different brightness levels. I can control it with my microcontroller, Muahahah! The question is now, where do i put i in ;-)
Sometimes it is just funny to work things out. So it had a lot of fun "hacking" this thing and learned a lot.
Take a look in the trashcan and make something with it!
Hope you liked my little howto.