Universal Relay Board
The Applications are Limitless, So Get Your
Imaginations Into Gear and Have a Go!
your sensor, you can cheat a little by adding
a one- to 10-kilohm resistor in series with the
sensor, but also add an equal value to the
fixed resistor. Try some experimenting with
resistor values; you can get quite creative and
produce very wide or narrow windows for
temperature sensitivity, etc. Just remember
sensor current ratings, though. Remember to
maintain a 50/50 sensor/resistor ratio for
better ±VR1 rotation.
Table 2 shows some examples of thermistor resistance/temperature resistances.
Don’t forget to replace C1 after setup.
If you are interested, the relay can be
made to self-latch by taking the spare pad
between the relay and VR1 and connecting it
to one of the relays’ normally open (NO) terminals. Linking pads are provided onboard.
The matching “C” common terminal is then taken to the
Neg supply rail. By doing this, you effectively bypass the
FET Q1 after it has initially engaged the relay. You need to
insert a switch in this connection to break the circuit to
release the relay and reset it.
The current rating of the left-hand set of relay contacts
is only rated at around two amps due to the circuit board
Possible uses could include:
• Battery protection for cars, low voltage accessory cutout
• Battery charger (NmHi, NiCad, SLA) cutout/warning, heat monitoring, overvoltage
• Baby monitor using microphone input
• Garden light controller, sunset activation
• Aquarium/incubator heater control or failure warning
• Power failure warning (battery backup supply needed), use voltage divider input
• Fire warning, connected to security system
• Intruder sensor, use LDR/LED beam, etc., in a security system
• Hand clap activated switch, breaking glass sensor in a security system
• Peltier device control, fridge, or incubator
• Garage door opener (LDR in a tube), set to activate with car high beam lights
• Voice-activated switch for an intercom, CB radio, transmitter, etc.
• Computer automation of other devices using logic voltages
• Toxic gas detection using a metal oxide range of gas detection sensors
track width. The circuit draws just under one mA at 12
volts on standby, 45 mA with the relay and LED on, and
about 62 mA if you use the latching option when the FET
Note: For best results, use a regulated power supply, with microphone option especially. NV