After acquiring a large ( 26cm x 13cm) 4 digit 7 segment display, from George (M1GEO) and not wanting to unpack I set about making it work under linux.
The board contains a SAA1064 - an I2c 4 digit 7 segement display driver chip. Ideal for connecting to my bus pirate.
After much stumbling around and trial and error I managed to get it to light each segment. The notable points(errors) were:
- I2C is an open collector bus, meaning each device only pulls the data lines low. This meant that I had to turn on the Bus pirates on board pull up resistors, as for some reason the ones I thought were doing it on the board weren’t.
- When using the bus pirates pullup resistors, the Vpu(V pull up) lead should be connected to +5V.
- The board requires a large voltage inorder to get the Led’s to light, my initial attempts used the bus pirate to power it, but this was both too low current 125mA and too low in voltage for anything to light. I then connected it to an external power supply and found it lights best at about 12V although the chip does get a little warm :S (The data sheet claims it’s good till 18V)
- The digits are counted from the right hand side(with the chip and sockets at the bottom).