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Weatherproof Touch Switch Simple Electronic Projects with Julian Edgar We’ve seen weatherproof switches, and we’ve seen touch switches. But have you ever seen a 100% sealed touch switch with no traditional moving parts that can be operated even while wearing gloves? W hile browsing the parts in an electronics surplus store, I came across a sealed metal disc, complete with an inbuilt LED. It was about 40mm in diameter and about 15mm deep. It appeared to be designed for panel mounting, and used a large retaining nut. Two pairs of wires escaped from the fully potted rear surface. The store owner said something about “piezo”, so I assumed it was a piezo buzzer with an inbuilt LED. I really wasn’t sure – but I bought a few anyway. When I got them home, I looked at them more closely. A tag on one of the wire pairs said “Everswitch” and then gave the LED’s voltage rating: 5V. There was also a separate 24V AC/DC 0.2A rating. This didn’t look like a piezo buzzer – maybe it was a switch? Pressing on the front face of the disc gave no apparent movement – so it wasn’t a microswitch. One pair of wires was colour-coded red and black, probably for driving the LED. The other two were both red, so they had no apparent polarity. Maybe it was a capacitance touch switch? But where Fig.1: the manufacturer’s (Everswitch) block diagram for the piezo touch switch. The LED part is easy to understand, but what on earth powers the control circuitry and solid-state switch? Read on to find out! 78 Silicon Chip was the power supply? This was sure getting confusing! I then searched for the part number and found that what I’d got was a pair of “touch metal piezo switches”. I even found a circuit diagram showing how to use the switch (Fig.1), but I am afraid that confused me even further. Yes, the red/black pair was to drive the LED; great. But the other part of the diagram appeared to show a piezo crystal connected to an control circuitry that in turn drove a switch (presumably a solid state one). But again, where was the power supply for the control circuitry and switching transistor? Then I discovered the answer. Piezo switches internally generate their own power from the deflection of the crystal. Amazingly, this provides enough power to operate the internal electronics. Lo and behold, when I checked the continuity across the two red wires, yes, they were connected when the face of the switch was firmly pushed. The switch stayed closed until the electrical charge dissipated – for a quarter of a second or so. So with the Everswitch, we have a completely sealed, weatherproof Photo 1: The mystery object – a 40mm diameter metal disc with... Australia's electronics magazine switch that can cope with a wide temperature range (-20°C to +75°C) and has a basically unlimited life (50 million operations, apparently)! Now that I knew what to look for, I found that metal piezo touch switches are widely available. They’re priced from about $8. I thought the best application for the piezo switch was a completely weatherproof switch to be positioned outside, possibly in the rain, snow and searing heat. It could operate a mains-switching relay through a latching circuit – one press to turn the relay on, another to turn it off. That’s when I discovered a second exciting and synergistic product. A bistable switching module Available via eBay and similar sellers, it is a very effective and tiny module. Find it by searching for “bistable flip-flop latch switch module” or similar. Ensure that the one you buy looks exactly like the one pictured. The cost is from about $5 delivered, and the main board is just 14 × 11mm. It comes with the header fitted and ready to connect. Photo 2: ... two pairs of wires coming from the rear potted surface. It turned out to be a fascinating device – an internally powered piezo touch switch. siliconchip.com.au Photo 4: The piezo touch switch, tiny flip-flop module and a mains 6V relay. With these components and a short amount of time, you can easily make a completely weatherproof switch that can even be operated when wearing gloves. This module will operate from 3-18V and it acts as a bistable switch. The momentary closing of an added normally-open pushbutton energises the output, with another push switching the output off. The switching transistor can handle 1.5A and it has an in-built protective freewheeling diode, so inductive loads like relays and solenoids can be driven directly. Various trigger times can be set by soldering links between pads on the rear of the module. For example, required pushbutton ‘on’ times before the module triggers can be set at one, two or four seconds. However, as bought, the module worked perfectly with the piezo switch as the momentary input. Completing the circuit All that is then needed to complete the circuit for a mains switch is a relay and a power supply. In my case, so that the 5V LED in the piezo switch could be operated, I selected a 5V DC plugpack power supply. I also chose a relay with a 6V coil – it works fine on the slightly lower supply voltage (the ‘pick up’ voltage of a 6V relay is typically around 4.5V). Fig.2 shows the resulting circuit. If you are using the relay to switch mains voltages, ensure that the relay is rated appropriately and insulate all mains connections. The relay should be mounted in an insulated or Earthed enclosure, with cable clamps or glands fitted to prevent the mains wiring from being inadvertently pulled out. Of course, a mains switch is only one potential use for this combination of the piezo touch switch and flip-flop module. Given that the flip-flop can handle up to 1.5A, it can directly drive low-voltage loads up to 18V. The current consumption of the piezo touch switch is zero (I still find that hard to get my head around!) and the flip-flop module draws only 2µA in its quiescent state and 2mA when its internal switch is on. These specifications lend the switch combination to battery and/or low-voltage renewable energy projects as well. Photos 5 & 6: The front and back of the tiny flip-flop module. The module will work with any supply voltage from 3-18V and can carry up to a claimed 1.5A. It can even directly drive relays. for security, or to simply give a very sleek product design. And, talking about security, if you want a hidden switch to release an electronic lock or switch off a burglar alarm, again, the piezo touch switch is ideal. Finally, metal piezo touch switches are often used in commercial applications where vandal-proof switches are needed. Another option After building this, I came across similar switches on AliExpress (1005003286484536; siliconchip.au/ link/ac4p); one is shown in Photo 3. They lack the LED but are available in three sizes and two finishes for around $6 each plus $9 for delivery. I think they are really good – epoxy sealed, with lower finger pressure required to trigger them than the one SC I bought earlier. Other uses Photo 3: this piezo switch from AliExpress is easier to operate and well-sealed but has no integral LED. siliconchip.com.au Because the required deflection of the piezo switch is imperceptibly small, it can be positioned behind other surfaces to disguise its presence. For example, it can be located behind the plastic front panel of a piece of equipment, giving a completely hidden on/off switch. The 200-400g pressure needed to activate the switch easily flexes the panel sufficiently. Such a hidden switch can be good Australia's electronics magazine Fig.2: the circuit for the mains switch. Note the orientation of the flip-flop module with the two components on the front face. The momentary touch switch triggers the flip flop – one press to switch on its output, and another press to switch it off. January 2026  79