precipiSTATION Controller Schematic
The sprinkler controller PCB consists of a switching power supply that converts the input of 24VAC to about 5VDC (exact VDC not important since the Particle Photon subsequently regulates it down to 3.3VDC); 16 identical optocoupler/triac drive circuits, one for each sprinkler station solenoid; two 8-wire-to-board terminal blocks, providing one power connection for each station, plus a 5 wire-to-board terminal block for common returns; a 2-wire to board terminal block for connecting 24VAC; indicator LEDs; socket for Particle Photon, along with 2 74HC595 shift registers; an unpopulated expansion header.
The board PCB wire traces for each channel can accommodate up to 1 Amp of current. A typical sprinkler solenoid takes about 250mA while running, with a turn on surge of about 500mA. The 24VAC input connector and 24VAC traces that feed the triacs can accommodate up to 15 Amps, so this board could theoretically be used to drive up to 16 solenoids at once, with the right VA rating on the 120 VAC to 24 VAC power transformer.
The switching power supply circuit is adapted from TI's Webench site, and uses the LM16006 (Digikey part LMR16006XDDCR). The optocoupler/triac circuit can be found in many sites on the internet (some with slightly different R and C values). It uses the MOC3063 optoisolator in conjunction with the Littlefuse L4N3RP triac (Digikey part number L4N3RPCT-ND). 180 Ohm and 1K Ohm resistors in conjunction with a 2N3904 turn on the optoisolator when a Photon output is high.
A downloadable .pdf of the schematic, and the National Instrument's MultiSim schematic file are at bottom of this page.
The board PCB wire traces for each channel can accommodate up to 1 Amp of current. A typical sprinkler solenoid takes about 250mA while running, with a turn on surge of about 500mA. The 24VAC input connector and 24VAC traces that feed the triacs can accommodate up to 15 Amps, so this board could theoretically be used to drive up to 16 solenoids at once, with the right VA rating on the 120 VAC to 24 VAC power transformer.
The switching power supply circuit is adapted from TI's Webench site, and uses the LM16006 (Digikey part LMR16006XDDCR). The optocoupler/triac circuit can be found in many sites on the internet (some with slightly different R and C values). It uses the MOC3063 optoisolator in conjunction with the Littlefuse L4N3RP triac (Digikey part number L4N3RPCT-ND). 180 Ohm and 1K Ohm resistors in conjunction with a 2N3904 turn on the optoisolator when a Photon output is high.
A downloadable .pdf of the schematic, and the National Instrument's MultiSim schematic file are at bottom of this page.
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