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



Hi Ray,

Thanks for taking the time to look at the substitute parts.

3) Q1-8 the N-MOSFETs should all be AO3400,
For some reason I had it in my mind that the 74HC595 latch was using 5V Vcc, but you are correct it using 3V3, so the N-Mosfet will be limited to 1A which might be a bit low, not really sure of the inrush current required to turn on the average solenoid.

I too was surprised that the AO3400 is not available from Element14
This seems to be Element14 substitute so I might go with it

4) Booster circuit optimized for 5V input.
I have been scratching my head trying to work out how you came up with the component values.
OSDC uses RT 27K and RB 1.6K, CT 330pF
OSBEE Uses RT 75K and RB 4.7K, CT 470pF

Using this calculator I get close to your values for OSDC, using a 9V input (OSDC transformer)
I guess I will go with these and can adjust if need be.

Using these values for input
Vin 9V
Vout 22V
Iout 55 mA
Vripple 1.8 mV(pp)
Fmin 77kHz

It calculates the below, of note are the R1 and R2 which are the voltage divider for the comparator are way off from your values for OSBee R1 and R2?
Ct=325 pF
Ipk=294 mA
Rsc=1.02 Ohm
Lmin=221 uH
Co=2236 uF
R=180 Ohm
R1=1.2k R2=20k (22.08V)

Thanks again.