audio-talk

Bought a Topping E30 II DAC to go on the end of a Roonbridge (running on an old 2008 Macbook with Debian Linux, the MacOS it'll run is well out of support by now). Due to arrive today. This is a temporary measure to quickly get Roon working with the hifi, as well as allowing me to exercise the DSD u...

Yep, I saw that in the sheet, but not sure how long that pulse lasts as its only for the duration of the write signal, but if that was the case then why won't it drive your two inputs? Anyway, you know how to fix it so its just tilting at windmills. Indeed, it's all finalised now - the parts order ...

I got some further feedback from AMB which goes some way to explain why the thing works reliably with 47k pull-ups, (but I'm still resizing them on the new board). Yes, you're right. I forgot about the effect of R2 which is effectively in parallel with the relay coil in series with the R2 on the opp...

I just did a quick spreadsheet based on those calculations, putting the numbers in for the standard issue boards and comparing the results with my modified setup and 10k pull-ups. So yes - the standard setup will (and does) work, with a whopping 11mA headroom on the output, by my calculations. And t...

5v across 47k gives you 10ua, so 110 < 163, so I would say its not a good bit of design IMHO. Not that the 5v is across the 47k is correct, assuming 1.2v for the two PN junctions in the darlington, that means its 3.8v across 47k + 2k7 so 7.7ua. Have you missed a decimal point there - I make those n...

Well here's the reply I got... Each "gate" in the ULN2803A is a darlington pair that has a Hfe of around 1000. It needs to pass 22mA at its output (collector) which is the rated coil current of the relay. Add about 3mA for the LED makes it 25mA. So the input (base) current into the darling...

Merlin Blencowe (I think it's him - the Valve Wizard) has a good article on the Valve Wizard website about fusing HT secondaries - I've had fusing on both of the 300B amp's HT secondaries from the get-go based on the advice given therein - which probably saved my mains transformers when I miscalcula...

Indeed, looks like I forgot about that a second time! I've asked the question. There is one reason I can think of which I included in my post - the system is designed to support up to 4 relay boards with two port expanders on each one, so that's potentially 8 PCF8574's, all of which have their ports...

I would ave just soldered the four resistors on the back of the PCB leaving the 47k resistors in place. Adding 1k or 2k2 or 4k7 in parallel with 47k is as close to be good enough. That would be good enough to get the four lines workign or at least see if I was talking tosh. I didn't think of that e...

Added in-line voltage drop resistor to connection for power relay which has a 12V coil I would have been tempted to use a 3v3 zener. See this kind of thing Nick is why you are a proper electronics engineer and I am a mere bumbling amateur. I haven't actually bought the part yet, I guess I just put ...

Did you not try my suggestion of changing the value of the pull up resistors? I still think 47k is wrong even in the case of single input single output. Would/might have avoided a new board. I have not, but there was a genuine reason for that - I can't get my side cutters in, the resistor networks ...

Revised PCB design completed and sent off to JLCPCB. This time I made it a four layer board and revised some bits of the layout which made things a little more elegant. There is something quite lovely about a well-laid out circuit board. https://user.fm/files/v2-70c6253bc643969d725c7ee718dd3671/well...

So not-so-happy days - we've proved the issue is the paralleling of the inputs to the darlington array from the port expander - seems that if you do that with these particular chips, the darlingtons don't trigger. https://user.fm/files/v2-6602222a6bae22a0876c8514394690cc/New_Control_Unit_2022_Relay_...

Well, the issue is proved - seems the PCF8574 can't deliver enough current in this circuit to trigger two darlingtons at once - it has to be one per port. I added some test diagnostics to the software which enabled me to probe around with a multimeter, and I got to the point where I could see the tr...

Nick wrote: ↑Wed Jan 04, 2023 3:07 pm Ok, so is it a bug that's causing the processor to reset?

The processor is absolutely fine - the issue I mentioned happened several months back when I had it in that build with the switched mode supply. In this build, the software is running perfectly, no apparent glitches.