Stepping Up to the Next Phase!

A project log for WITCH-E Decimal Based Computer

Document and create a modern replica of the Harwell Dekatron computer known as the WITCH

Dave's Dev LabDave's Dev Lab 11/24/2017 at 02:080 Comments

After getting Phase3 working with the 5-wire input system, the next step is Phase4 with the paper tape reader. I've not completed Phase3 yet, but I am close, so it's time to start doing some more prep-work for Phase4. I got a 3" (80mm) printer assembly off ebay a couple weeks ago. There are a number of these printer assemblies available as replacement parts. The one I select for testing is the Seiko LTP1245, which has a ton of clones available. It has a 5V 2-phase stepper motor that drives the pinch wheel for the paper. I found the Texas Instruments DRV8834 during some basic searches and it looked perfect for interfacing with my simple circuitry replication from the original tape reader interface on the WITCH. After a couple quick google searches for a breakout board for the DRV8834, I found one from Pololu that looked perfect for testing. Of course, for Phase4 of WITCH-E, I'll be designing my own boards for this, but during prototyping and testing this makes it super easy. One of the concerns in selecting a driver chip was that it was available in several packages. While I do have resources to work with QFN (Quad Flatpack Noleads) packages, I'd prefer to have something easier to solder by hand, and the DRV8834 is available in 24HTSSOP which I can easily solder by hand. Get to stepping!