OpenSprinkler › Forums › Hardware Questions › OpenSprinkler › capacitor value on OpenSprinkler 3.0 RTC and misc. errata for scratch build › Reply To: capacitor value on OpenSprinkler 3.0 RTC and misc. errata for scratch build
1) On the master PCB, the schematic shows 0.1uF for C4, but presume this is placeholder and is meant to be something else? I was getting odd RTC behavior until I noticed this. I’ve left it out for now, presume NTP will fix any drift anyway.
==> In the actual product, C4 is NOT populated. It’s there because it’s what the datasheet recommends, but it should be a very small capacitor that accounts for the PCB parasitic capacitance. It should definitely not be as large as 0.1uF, and in fact just leave it unpopulated.
2) Looks like the resistor LT and RL aren’t populated on master PCB?
==> These are not populated, you are correct. They are there to form a light sensor, because we use the same OpenSprinkler top-level circuit board for other purposes (RFToy WiFi version, a WiFi light sensor, and the WiFi thermostat that we’ve been working on). For OpenSprinkler, these are not populated at all.
3) On DC driver PCB, I missed that the final drive FETS were supposed to all be AO3400, I ended up using BSS123 since this is what pops out of BOM given not all parts are labelled correctly in Eagle. That was kinda dumb on my part since should have known BSS123 can’t handle that much current, but just putting it out there in case it helps others that likewise get confused.
==> You are correct it should be AO3400. Apologies for the inconsistency, I really should carefully check the component values before publishing them.