Computing stuff tied to the physical world

Running LED ticker

In Hardware on Nov 1, 2011 at 00:01

For a while, these “ticker tape” displays were quite the rage. They probably still are in shop displays where LCD screens haven’t taken over:

590996 BB 00 FB EPS

This one is powered from 12 VDC, and has a serial RS232 interface with a funky command structure to put stuff into its line- and page-memory. Lots of options including lots of scroll variations, blinking, and beeping.

Well, a friend lent me one a while back and we thought it’d be fun to add a wireless interface via a JeeNode.

Time to take it apart, eh?

It didn’t take long to figure out the way to hook up to it, and there was some useful info in this discussion from a few years back.

I decided to use this P4B serial adapter from Modern Device to interface the JeeNode to the RS232 signals:

DSC 2702

It’s convenient because it plugs right into the FTDI connector, and it has the onboard trickery needed to generate “RS232’ish” voltages. The whole thing is mounted on foam board using double-sided tape and the JeeNode can easily be unplugged to upload a new sketch.

Here’s the whole “mod” on the back side of the display:

DSC 2701

There’s a wire to the +5V side of a large cap, used to drive the displays no doubt. The JeeNode’s internal regulator will convert that down to 3.3V, as usual.

The positioning of the JeeNode is tricky, because the entire enclosure (apart from the smoked glass at the front) is metal – not so good for getting an RF signal across. I decided to place the antenna at the far edge, since the end caps are made from plastic. Hopefully this will allow good enough reception to operate the unit while closed.

The serial pins are conveniently brought out on some internal pads, right next to the RJ11 jack used for RS232:

DSC 2703

I haven’t hooked up RX and TX yet, because I still need to find out which is which.

I’ve verified that I can communicate with the unit through a USB-BUB wired through to the P4B adapter, i.e. straight from my laptop.

Next step is to write a sketch for the JeeNode…

  1. Why didn’t you use an uart plug?

    • The UART Plug has hardware support for serial I/O, but no level converters. Since the JeeNode used here has all its I/O free, I can simply use the built-in serial I/O.

      The P4B board converts 3.3V (or 5V) “logic levels” to voltage levels needed by a standard RS232 interface (it’s not the official -12 .. +12 V swing, but sufficient to work in most setups).

  2. Oooh, I remember pulling one of these things out of a skip outside work a few years back. It was only a boring RED one, and I never got round to playing with it.

    Now I wonder if I still have it, and if so, where on earth is it?!

  3. Where did you get the hardware?

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