• You WILL be integrated!

    Dave's Dev Lab6 hours ago 0 comments


    Well... after a few "blue wire fixes", I was able to test the Input Sequencer, Relay Set D Latch, Keyboard Encoder and the Manual Entry Keypad boards together! As noted in an earlier post ( One Down - Four to Go... Sorta ), I decided to only build up one of the Relay Set D Latch boards and I am glad I did! There were a couple minor mistakes on the board that I corrected with some blue wire. Now the question is: Do I Blue-Wire-Fix the rest of the boards, or do I correct the PCB and order new ones? Decisions... Decisions...

    Either way, despite the futile attempts at resistance, I have integrated them! 

  • Let Me Encode Your Keys!

    Dave's Dev Laba day ago 0 comments


    In my quest to get the input system working, I wired up the keypad and 5-bit baudot encoder to do some testing. I have it bread boarded with a little LED board I created to help with bread board testing that I call Dave's Breadboard Led Trinkit (BLT for short!). The encoding is not standard Binary Coded Decimal(BCD), but a variation of the 5-bit baudot code popular at the time the WITCH was built. I really could have made the diode steering board a lot smaller, but as I noted in another log post ( Keypad Encoder ), I had a bunch of vintage diodes that I thought might look cool to use...

  • One Down - Four to Go... Sorta

    Dave's Dev Laba day ago 0 comments


    As I noted in my earlier log post ( Something to Latch Onto! ), I need to assemble 5 of these Relay Set D Latch boards to do my full test of the input system. I took an hour this afternoon to assemble one and I started thinking... this is a lot of assembly, I better make sure these work before I assemble four more! So I have one completely assembled and ready to test. I'll go through and get as much tested as possible before building up the other four!

  • Something to Latch Onto!

    Dave's Dev Laba day ago 0 comments


    In the original WITCH, the input system uses 5 module blocks know as "Relay Set D". Each Relay Set D, consists of two basic sections. One section is used to latch and "store" a 5-bit baudot code, and a second section to decode the 5-bit baudot code into a "1 of 10" decimal signal. For the WITCH-E design, I've broken the Latch and a Decode sections of the Relay Set D into separate PCBs. For me to test the keypad, keypad encoder, and input sequencer, I need to have 5 of the Latch PCBs assembled and tested. Looks like I have my work cut out for me this weekend....

  • New Input Sequencer Assembled

    Dave's Dev Lab2 days ago 0 comments

    As noted in my earlier log post ( All Your Sequence Belong to Us! ), I had ordered and received some new Input Sequencer PCBs. After making that log post, I realized I didn't have enough parts to assemble the board, so I had to order some in from Digikey. The parts arrived this morning. I found some time this evening to do the assembly and get it ready for testing...

  • Steampunk Dekatron

    Dave's Dev Lab3 days ago 1 comment


    As I noted in another log post, my young friend Justin King worked on creating a javascript based WITCH emulator over the summer a few years ago. As a thank you for the work on the project, I wanted to give Justin a real Dekatron. I had previously found this Dekatron Spinner Kit on the net, and found the kit for sale on ebay, so I purchased an original GC10B Dekatron and a spinner kit. The kit is well designed and came with all the components ready for assembly. After assembly and testing, I thought to myself "Hey, this would look really cool in some sort of case!". After a little shopping at the local home decor store, I found this sweet little steampunk looking box. After drilling a hole for the Dekatron to extend through, I added a power switch and a potentiometer to adjust the speed of the spinner. I think it turned out pretty well, and Justin was very excited to receive it as a gift!

  • Getting Screwed: Finding Mounting Hardware

    Dave's Dev Lab4 days ago 1 comment

    For a project like WITCH-E, it isn't always "fun and games" with the electronics and research. Practical matters need to be addressed such as: How the heck do I mount all of these PCBs onto some acrylic? From a design perspective I wanted to use some very small screws to take up as little pcb space as possible. I also needed the method to be both easy and inexpensive as I would need mounting hardware for roughly 200 pcbs. My first thought was to purchase some off-the-shelf M2 screw kits with standoffs, then I did the math! Each box only contained 10 of the screws and standoffs that I wanted to use and at a price of around $6USD, that made each standoff with matching screw cost $0.60USD. Plus I would have to purchase 80 kits! So I continued to look. I found some inexpensive teflon spacers, and some 13mm long M2 screws at a decent price and decided on using them along with a matching nut. Well that was the plan... until I actually tried to use them. Threading the screw through the holes on each pcb while holding on the other screws and making sure the teflon spacers stayed in place was nearly impossible. So once again I went in search of mounting hardware. My first thought was to visit McMaster-Carr's website to see what was available. As recently posted on Hackaday.com (https://hackaday.com/2017/09/13/noobs-guide-to-mcmaster-carr/) McMaster-Carr has just about any kind of screw, nut, and mounting known to man in single quantities, and they had what I was looking for. Unfortunately, just like the kits, the M2 standoffs and screws were WAY too expensive to consider in larger quantities, so my next step was to try Ebay. After tweaking my search key words, BINGO! The pricing was much better, around $0.10USD for two screws and a standoff. So the moral of this little post is that buying the right mounting hardware can be tricky and that you have to be careful not to get screwed while trying to buy screws...

  • Dekatron Simulator Evolution

    Dave's Dev Lab5 days ago 0 comments


    The essential technology at the heart of the Harwell WITCH is the Dekatron. The Dekatron, as the name implies is basically a decade counter, and while many variations of the Dekatron are still available via places like Ebay, using them in the WITCH-E project was not economical, not practical, and generally not safe due to the high voltages needed to operate them. So what I needed was something that could replicate the functionality of a Dekatron. Something made with modern components, something that would be inexpensive to build (since I would need to build a LOT of them!), and something that was easy to assembly by hand. The first task was to find components that matched the functionality of the Dekatron as they were used on the WITCH. Dekatrons support the ability to increment their stored count as well as decrement the stored count, however in the WITCH the Dekatrons were only used to increment the stored count, so I focused on finding something that only supported incrementing. My first prototypes used a 74HC160 decade counter with BCD (Binary Coded Decimal) output connected to a 74HC4511 BCD to 7-segment display. This version was rather large, used two chips and needed 8 resistors, plus it just didn't "feel right". The 7-segment display gave a really good educational aspect to the design, but just didn't have the same "feel" as the  circular Dekatrons, so I went back to the drawing board. Again since I only needed the ability to increment, I selected the 74HC4017, a TTL version of the popular CMOS CD4017 decade counter. On the first revision using the 74HC4017,  I placed the LEDs on the front, with the 74HC4017 on the back of the board, making it a two sided assembly. My thinking was since I was hand assembling these, having a two-sided assembly wouldn't matter much... boy was I wrong! It really complicated the assembly process and made it very time consuming. So on the next revision of the design, I went with all single sided assembly. While having the 74HC4017 in the center does take away from the aesthetics on an individual PCB, the overall results for an assembled group are generally geeky enough to over look this minor issue...

  • It's All About the Datasheets!

    Dave's Dev Lab6 days ago 3 comments


    In the effort to translate and convert the WITCH design from using Cold Cathode Valves (aka tubes) into modern components, it was essential to understand how each of the valves worked and how they were being used in the system. As someone who grew up in the age of the transistor, I was completely unfamiliar with practical applications of using valves. This is where the engineer in me kicked in. The first order of business was to find datasheets on every component I could identify. The WITCH schematics and maintenance logs had very good details about the model and type of devices being used. I quickly found on the net The Valve Museum. Most of the parts I was looking for were documented there with datasheets and pictures! Now with datasheets in hand, I was able to start working backwards on how exactly these engineers created a working computer from "stone knives and bearskins"!

    EDIT: pictures and pdf datasheets are available via the WITCH-E Project github repository under datasheets

  • Getting Started! The WITCH Bootrom

    Dave's Dev Lab09/17/2017 at 02:32 1 comment

    One of the fundamental aspects of the WITCH-E project is to gain a better understanding of the the original WITCH and document it. Unlike many other retro computing projects where thousands, or tens of thousands of the original computer still exist, there is ONLY one WITCH. With that in mind, I can't really ask to "poke around" on the original, and randomly hook up logic probes, so I had to use a different method for reverse engineering the WITCH. Most of the details I have learned about the machine are from maintenance documents/logs, schematics, and pictures of the machine. One of the research areas I was keenly interested in is how the WITCH initially started up. Modern systems often use Read-Only-Memory(ROM) that contain the systems initial instructions, but what did the WITCH use? I made a short little video of how I figured this little item out, and replicated the functionality....