Bridge-Rectifier LED Indicator

Using a few diodes and a LED, you can make a nice indicator as shown in associated schematic diagram that can be used for a lot of applications (with a bit of luck). It’s quite suitable for use in series with a doorbell or thermostat (but don’t try to use it with an electronically controlled central-heating boiler!). This approach allows you to make an attractive indicator for just a few pennies.