Not everyone is going to be interested in the safety circuit. I have mixed feelings about that, but there isn’t a way to force the issue. Table saw manufacturers can’t keep people from removing the safety guard on the saw, this isn’t any different. I’ve removed the circuit from the main PLL board and put it on it’s own board. This also allows a lot more real estate on the main board, but I must stress the safety… splitting water is a hazardous business.
Files: wfc_safety.zip
I’ve worked out the design and the board, I’m working through the logic to make sure that it’s viable. It’s an ‘active live’ design, any failure causes a ‘fault’. A fault should occur if:
* wires are broken
* the optoisolators get burned out
And the more normal faults:
* low or high water level
* low or high pressure
Low water causes a fault, and also switches a relay for a pump or valve solenoid. Very low or high water, wow, that shouldn’t happen, especially high water. High pressure, yeah, definitely turn it off for a while. Low pressure: normal when the system is first starting, but what happens when there’s a blowout? You wouldn’t want this to just keep on running with a hole in the plumbing, so low pressure causes a fault. To get the system running, there’s a “pilot” momentary switch which defeats the low pressure fault, this is just like the pilot switch on a gas appliance, you hold it down for a minute while the system starts, then you can let it go as soon as there’s enough pressure to keep it running.
Parts list
| Qty | Value | Device | Comment/Digikey | Parts |
| 1 | 0.1uF | poly capacitor, 5mm lead-in | voltage regulation | C2 |
| 1 | 1K | 1/4 watt resistor, 10mm lead-in | R3 | |
| 1 | 1N4003 | regulator diode | or 1N400X relay coil clipper |
D2 |
| 1 | 1N4148 | small signal glass diode | or 1N914 | D1 |
| 1 | 2N2222A | NPN transistor TO-92 ( or TO-18 ) |
relay driver | Q2 |
| 1 | 2N2907A | PNP transistor TO-92 ( or TO-18 ) |
relay driver | Q1 |
| 5 | 4.7K | 1/4 watt resistor, 10mm lead-in | 5V pull-up resistors | R1, R4, R5, R7, R10 |
| 1 | 74AC02 | IC: Quad 2-input NOR 14-DIP | 74AC02PC-ND | IC1 |
| 1 | 100uF | electrolytic capacitor 8mm with 3.5mm radial leads |
voltage regulation | C1 |
| 4 | 330 | 1/4 watt resistor, 10mm lead-in | LED current limiters | R2, R6, R8, R9 |
| 1 | G5V-1 | Omron G5V-1 RELAY SPDT 5V 167 OHM COIL |
water pump switch Z773-ND |
RELAY1 |
| 1 | LTV-847 | Quad Optoisolator 16-DIP | 160-1370-5-ND | OPTO1 |
| 1 | SPST | Normally open SPST momentary contact switch |
for “pilot” | S1 |
| 4 | Fuse clips | for ATO fuses | F067-ND | F1, F2 |
| 1 | 1A ATO Fuse | for logic circuit | F1 | |
| 1 | 10A ATO Fuse | for cell circuit | F2 | |
| 1 | MF-R040 | PTC Resettable Fuse 400mA hold, 800mA trip |
logic circuit protection MF-R040-ND |
PTC1 |
28-SEP-2008 Added fuses and PTC. Board will fit 90mm spaced holes. Schematic, files and pictures updated.
01-OCT-2008 I got the relays, tested that part of the circuit, and it’s good. The ATO fuse clips look really good, I’m happy with the way that turned out. Files and schematic updated, this is the version I’m submitting for manufacture to Sierra Proto Express . It’s been accepted and is “in progress”. 6 boards should be here 09-OCT-2008.
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