The circuit is powered by a 9v 9v battery. With each tap of a finger to the box holding the wafer, the circuit turns on and off AC or DC power to an external device. Circuit by David Johnson P.E.-July, 2017įinger Tap Piezo Relay - This circuit uses a flat piezo wafer, glued inside a plastic box, as a finger tap sensor. Others flutter badly during the dawn and dusk switching transitions, burning out compact fluorescent lamps, which do not like rapid power fluctuations. Some commercial switches are not sensitive enough to detect when the sun is out. These switches turn on a light during the night, then switch them off during daylight hours. Hobby Circuit designed by David Johnson P.E.-July, 2011ĭusk To Dawn Latching Relay - Over the years I have had to replace many dusk to dawn switches for outside lights. The solid state relay provides 5KV isolation from the computer. A small solid state relay turns on and off the relay. The circuit uses a power relay with a 120vac coil and 10 amp contacts. The circuit below shows how this could be done.

Circuit by Dave Johnson P.E.-May, 2009Ĭomputer Controlled Power Relay - Often there is a need to turn on and off a 120vac device using a low power +5v logic signal from a computer. One LED forms a red light source, which illuminates a second red LED.

It is fully isolated using two inexpensive red LEDs. Dave Johnson, Lubbock TX-DC Magazine - Issue īidirectional Solid State Relay - The circuit below can switch up to 4 amps of current with a peak voltage up to 20v. The circuit is a simple relay driver powered by a9v battery. Four wires leading from plastic junction box would connect to a second box containing the touch switch module. (1) A relay is mounted inside a plastic junction box and (2) a touch switch module. The total light power is less than 100 watts. When touched, a string of fluorescent or LED lights, mounted under the cabinets, would turn on. The unit needed to be fairly small and wired into the underside of some kitchen cabinets. Hobby Circuit designed by David Johnson P.E.-June, 2000 Battery_Powered_Touch_Activated_Latching_Relay - A client needed a touch activated switch. The relay hobby circuit shown below demands only 50uA of input current. But such current levels often force battery powered circuits to use excessively large batteries. :ĥ0ua Current Drives Solid State Relay Requires Only - Most solid state relays require at least 5ma and often more input control current, to fully turn on the device.

Auto turn off relay circuit