The new black PCBs arrived this morning! Unfortunately my day job is going to keep me super busy this week, so it might not be until Friday evening before I get a chance to assemble some. I went with black soldermask in the hopes that the dark background will make the orange LEDs stand out more, and make the decade counter IC in the middle blend in more with the background. I like to order my prototypes from pcbway.com which offers 10 pcbs (100mm x 100mm or less) for $5. They also offer a range of soldermask colors at no extra charge. These will be hand assembled, so I went with HASL instead of ENIG. If I had planned to assemble these on the Pick-n-Place machine, ENIG is preferred.
This is one of the early prototypes of the Dekatron Simulator. As you can see from the video, the Dek-Sim on the right, triggers the Dek-Sim in the middle once it has reached the zero postion, and the one in the middle triggers the one on the left. This version of the design required each of the Dekatron Simulators to be powered and a wire connecting the output of one into the input of the another. In the new design, the connectors on the sides of the Dekatron Simulator are designed to pass ground, vcc, and the ouput to the Dek-Sim on the left. This will make it easier to daisy chain the modules to create displays for devices such as frequency counters with minimal wiring.
Since Dekatrons are decade counters, they make perfect sense to use in things like frequency counters. This is a short video of a restored Dekatron base frequency counter. More information on this restoration can be found HERE!
The essential technology at the heart of the Harwell WITCH is the Dekatron. TheDekatron, 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...