How do you guys verify schematics before sending to prototype fabrication? I am still learning electronics so I do not allways have full confidence in my schematics (with good reason).
So far I have been posting on this forum, but I dont know if it will work for me to just keep spamming Hugo and you other guys ;).
Is there some service that makes sense, where I can pay to get my schematics and PCB layouts looked through / verified, before i order the 5-10 first assembled prototypes?
I would like to do this, because it really sucks having waited 20 days and payed money and then I get something from PCB manufacturer that does not work, because i made some error to the schematic or so.
For instance i made a board with minute changes to the jane so that it could support a 5V water-flow sensor. And i changed terminals to that each relay has a “NO” and “GND”, so it fits my application.
However getting a 10pcs quote from Circuit hub it costs 1000USD+ and takes 18 days without shipping to europe. So being sure that it actually probably works before i send it out, would be really relieving :-).
I haven’t used it, but other community members have: https://oshpark.com/ Looks a lot less expensive, and better suited to small-volume trial runs too.
www.pentalogix.com will fabricate PCBs in 1-3 days. I use that service regularly. Its not cheap, but its quick. The cheapest way to populate a board is to do it yourself. Get a good soldering iron and hot air rework station. Both can be had for under $100 each.
Ok so order all the components to where i work, get some PCBs without components fabricated, assemble it and see if it works… Sounds like an ok plan :-). I already have access to both soldering iron and hot air gun from Weller
1000USD for 10 boards is close to theft. Use Eurocircuits or similar services in Europe to get 10pcbs at a fraction of that cost. Standard service delivers in 7 working days.
Andrew Co-Founder of CircuitHub here. It’s important to point out we only quote on full turnkey assembled PCBA’s.
For an apples to apples comparison you’ll need to look at the cost of the parts, plus board and assembly. Also remember lead time’s are additive, if you use a PCB pooling service on a 12 day lead and 10 day assembly you’ll get the boards back in 22 days + delivery.
If you can find a lower cost equivalent service to CircuitHub I would love to know.
For small orders i have gotten cheaper quotes from ITEAD PCB due to their low assembly price. However they resently had a problem with a component supplier sending fake chips, so right now I would have to buy the components and get them shipped to ITEAD PCBA team. So in this case I would rather use your service, which is just recently became aware of. The only thing i don’t like about it is that when living in EU, it is always easier with tax, regulation and such, when things are from inside EU :-).
I’ve been using pcbnet.com for my PCB boards. I’ve found their prices to be pretty competitive. They manufacture the bare 2-layer boards and I populate the components. However, I’m also pretty certain they do complete fabrication if you’re interested. I also believe they’ll do a layout check, but you’d want to confirm that.
Yes it is funny to make the schematics but also It often takes 14 days and some money to get assembled prototypes, which is why it is Nice to get the design somewhat verified before ordering.
So what do you say, does my modified Jane schematics look sane?
Can’t see what transistors you’re using for Q1-Q8; you should check the voltage rating (many small FETs top out at Vds=20V).
As you’re running some high current stuff off the half-wave rectified rail, it’s possible you may need to increase the size of C5 to be able to (eg) drive multiple relay coils at the same time.
I would add some resistance to R99 (as no current should flow there) and also a 3.3v zener to ensure the input is clamped at 3.3v.
Does the flow sensor really need much current? A high voltage LDO might be cheaper.
Can’t see what transistors you’re using for Q1-Q8; you should check the voltage rating (many small FETs top out at Vds=20V).
The FETs Q1-Q8 are the ones used in the original jane design, posted in your reference design section, NXP 2N7002P,215 rated at 60V.
As you’re running some high current stuff off the half-wave rectified rail, it’s possible you may need to increase the size of C5 to be able to (eg) drive multiple relay coils at the same time.
C5 is also from the original jane design, but i see your point about driving multiple relays, and this might come in handy later. My intended purpose with this relay board is to drive a bunch of solenoid valves, however only one at a time to maintain water pressure (they are on the same main pipeline)
I would add some resistance to R99 (as no current should flow there) and also a 3.3v zener to ensure the input is clamped at 3.3v.
I have added a 330 Ohm resistor in series with R99 as you suggest. And a Zener (CD0603-Z3V3) to clamp input. Good idea, thank you! Is 330Ohm sensible? I was unable to locate max allowed current to GPIO pins in datasheet.
(The reason why i added R99 as a 0-ohm jumper resister, was so that I could disconnect all the stuff on the jane that I added if it was somehow failing ).
Does the flow sensor really need much current? A high voltage LDO might be cheaper.
NO not at all, good point, the sensor requires like 8mA. I just went for the LM25007 because it was already a component used in the design, so i thought i “safe” to pick that one. I will be looking for a cheap LDO instead.
I’d go for 1k at least. Really, only microamps will flow in the IO so you can be generous with the resistor.
Try the TPS79801. It does 50mA at up to 50v (though: note heat dissipation when you’re dropping that far! 25v drop at 8mA = 200mW). Used it on the nest prototypes.
Swapped the resistor for a 2k, the 330 ohm was inspired by raspberry Pi GPIO circuits.
For now i will stick with the LM25007 because I need to get some prototypes fabricated asap, for next revision I will consider the TPS79801.
Out of curiosity, what is running at such high voltages in the Nest?
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