most modern design for an HP41 rom module?

[John Ioannidis]

(08-06-2024 03:15 AM)Monte Dalrymple Wrote:  

(08-06-2024 02:34 AM)John Ioannidis Wrote:  Thanks, but not useful if you don't publish the software! I'd be making my own PCB anyway.

While we are at it, why use the combination of 4050 and 40109 to do the level-shifting, instead of just a TXB0108 or an SN74LVC8T245? Are the bidirectional signals open-drain, and only need to be pulled down, in which case something like https://www.adafruit.com/product/757 with weaker pullups would do the trick?

/ji

Both the TXB0108 or an SN74LVC8T245 are 5.5V max. The 41 bus is 6V. The 40109 has much better supply current also.

Ah, that explains why I had used a bunch of BSS138 with pullups (like in the adafruit circuit I referenced) when I needed to go between 3.3V and 12V in a recent project. I'm so used to going from 5V to 3.3V, and occasionally down to 1.9V that I forgot about the upper limit

What do you use to make your boards? I use jlcpcb.com, and also use their assembly service for placing passive components. They are really cheap, and still very high quality. A recent order of five boards, ~150x50mm, four layers, ENIG finish, each with about 20 resistors and capacitors and six transistors, were around $60, $17 being the cost of parts+assembly. Definitely worth it. They don't have a good selection of ICs in stock, but I can still hand-solder down to TSSOP, so that's not a problem.

I don't have any affiliation with them other than being a very satisfied customer.

Here is an example (in this case, they happened to have the ftdi chip in stock, so I only had to solder the IR LED) https://www.hpmuseum.org/forum/thread-20143.html