Flip-dot Display

13 March 2014

I've got my hands on 6 flip-dot displays through an eBay auction.

  • 1 old Bright Tech, I've not looked at this yet but it has a fluorescent tube light in it
  • 1 small Hanover (20 x 7 dots)
  • 2 Bright Tech Bright Dots (95 x 16 dots)
  • 1 Bright Tech Bright Dot (90 x 8 dots)
  • 1 Bright Tech Bright Dot (20 x 14 dots)
  • 1 Bright Tech controller of some sort

Not knowing much about them other than what I could discern from the Wikipedia article I'm endeavouring, first of all, to make them function in their current state.

Interfaces

The front of the controller and display are fairly non-revealing: Front of controller and display

The rear are where the connectors sit, but unfortunately I have no cable to run between them and no pin-outs to determine what should connect to what. Opening them up to take a peek at the innards is helpful though, after a quick Google for some of the various IC's (integrated circuits) involved.

The 3 important parts of the display board are the power, the data, and this IC. Display board

The PCB is marked up with "power input (24v)" by the bottom connector. I do not have a 24 volt supply to hand, so 12 volts will have to suffice.

And suffice it does, the video above shows the power up sequence when 12 volts are applied to that cable.

The SN75176B IC is an RS-485 tranceiver, so the communication is likely done over an RS-485 bus. The 2 pins used for communication are A and B, these should be wired up to the matching A and B on the controller. A helpful little multimeter revealed both of these wires in the cable.

I've highlighted the corresponding parts of the controller board too and with the multimeter found the correct pins in the external connector: Controller board

I cut the P4 power connector off an old PC power supply in order to get a data connector for the controller side.

Testing

I plugged it all together, powered it up, and... nothing :-(

As I change the selection on the controller I can hear the display whining as though it's powering through all of the dots, but they're all being set to off. I'm wondering if this is because the big messages are intended for the large display at the front of the bus and this is only a rear number sign. Flicking through to find a message with a number in it still doesn't show anything on the display though.

Now I'm wondering how the controller would even know not to send the long message to the rear sign. There must be some sort of addressing used in the protocol and these DIP switches look a likely culprit for setting the address of any given display: DIP switches

If this does represent the address then it's currently set to 3. Let's see what changing it to 1 does: Display showing "So"

As seen in the picture above, it's now a little bit less broken. It's displaying the first 2 characters of "Sorry Not In Service". From this I'm assuming that the DIP switches are in fact some sort of address, and that address 1 is probably for the big signs from the front of the bus. This is the only message that displayed anything though, I'm a bit confused about this.

Next Step

Next up I need to figure out the communication protocol that's going over the RS-485 bus and see what's going on a bit more. I'm hoping I'll see messages being sent out for more addresses that I can then select on the DIP switches. In order to do this I've ordered a USB RS-485 dongle. Once it's arrived I'll be diving straight back in to this.