The HM Digital PM-1 is the board-level OEM version of HM Digital's purity alert: a bare circuit board plus in-line sensor, intended to be built into a water cooler, vending unit or enclosed purification system rather than mounted on a wall.
It watches for TDS creeping above the service threshold and raises a warning light (red or yellow, steady or flashing) with an optional 20-second audible alert — a filter-change indicator the end user cannot ignore. Mains powered, so there is no battery to service.
| SKU / Model | PM-1 |
| Product Type | OEM board-level in-line TDS purity monitor / alert |
| TDS Range | 0–200 ppm (mg/L) |
| Set Point | Dip-switch selectable, 2–198 ppm in 2 ppm steps (10 ppm default) |
| Accuracy | ±2% |
| Calibration | Factory calibrated |
| Alert | Warning light, optional audible alarm |
| Light Colour | Red or yellow |
| Light Function | Steady or flashing |
| Alarm | Beeps for 20 seconds |
| Power Supply | AC 110 V / 220 V |
| Cable Length | 62.86 cm (24.75") |
| Circuit Board Dimensions | 8.9 × 6.9 × 3.8 cm (3.5 × 2.7 × 1.5 in) |
| Weight | 266.5 g (9.4 oz) |
| Warranty | 1 Year Limited Warranty |
Specifications transcribed from HM Digital’s published PM-1 product page — HM Digital does not publish a full manual for the PM-1, only the dip-switch setting sheet linked below.
📄 PM-1 Dip-Switch Instructions (PDF)HM Digital publishes no full manual for the PM-1 — this is their dip-switch setting sheet, which gives the switch pattern for every set point from 2 to 198 ppm in 2 ppm steps. Published by HM Digital, Inc. For figures not covered by it, please confirm with us before designing the PM-1 into an assembly.
