OpenSprinkler Forums Hardware Questions OpenSprinkler Pi (OSPi) Smaller DC version of OSPi Reply To: Smaller DC version of OSPi



1) 220uH inductor: your RLB0912-221KL should be fine. I don’t really have any specific numbers for the current and resistance values, but I think it should be rated 330mA at minimum (because the 1 ohm current limiting resistor that goes with MC34063 limits the current to 330mA). Since the booster is only turned on for a very short period of time, the inductor current isn’t as critical as in situations where the booster needs to remain on constantly.

2) Yes QP1 and QP2 are AO3401, not AP3401 (and should not be BSS84 because BSS84 cannot handle high current). Your DMG2307L seems a suitable substitute.

3) Same, the N-MOSFETs should all be AO3400, not BSS123. Your ZXMN3F30FHTA seems ok. The only concern is if you look at the Drain Current output characteristics, under 3.3V Vgs, the current seems to saturate at about 1 amp. This performance is worse than AO3400. Still, if your application doesn’t require more than 1 amp of current, it should be ok.

I am a bit surprised that AO3400 and AO3401 are not available where you are — these are quite common parts.

4) I don’t think the Booster circuit needs to be optimized — it should work pretty well under a wide range, at least 5VDC to 12VDC. You said “I notice you different values in the OSBee for the capacitor and resistor around the 34063 boost converter.” can you be more specific about the different values? A few quick notes:
– If you mean the current limiting resistor, I’ve frequently used 1 ohm. It can be higher or lower, the tradeoff is that higher resistance leads to lower current, so it takes longer time to boost but the plus side is that you can use smaller inductor since it doesn’t need to run high current; conversely, lower resistance leads to higher current, so it’s faster to boost, but the inductor needs to withstand higher current.
– By capacitor I suppose you mean the timing capacitor. It (together with the 180 ohm resistor) controls the switching frequency and this can really vary a lot. For example, the capacitor can be anywhere between 150pf to 470pf; resistor can be anywhere between 100 ohm to 470 ohm. There isn’t any one set of correct values.