Solution: Often, I am reclining on my bed with my laptop, (see easylaptopstand), so I decided to build a remote access power resetter (see first picture) with an Arduino clone. I can aim my laser pointer at the resetter and it will automatically cycle the power on the radio/antenna.
Phototransistor: Digikey SFH310 $ 0.38
Relay: Digikey Z146-ND (G2RL-24DC5) $3.22
LED book lamp: Dollar store
Laser pointer: Dollar store
Anarduino (Arduino clone): Ebay $18.90 for 2
USB-BUB: seems to be cheaper at Wulfden $16
Step 1: Simplified Electronics Theory
A phototransistor is basically an on-off switch like a light switch or a pushbutton. But it’s controlled by light instead of mechanically pushing the button. When light illuminates the phototransistor, the two leads will (basically) be shorted together. When the light is removed the two leads will be disconnected. (see picture)
Specifications: The specification that is most significant is whether it is an NPN or PNP. My design is based on an NPN phototransistor. The data sheets have a lot of information about wavelength, sensitivity and (collector) current. Unless you are designing for a specific application, these shouldn’t be that critical. Most phototransistors will respond to typical light sources like LEDs and laser pointers. One thing you may need to worry about is the distance between the light source (especially an LED) and the phototransistor. With the LED and phototransistor, I had, they had to be within about three inches of each other. That’s why I decided to use a laser pointer where I can be across the room.
A relay is (usually) an electromechanical switch. (See pictures) The relay is the upper part of the drawing. The little curly cue thing is the coil. It is an electromagnet that is a magnet when voltage is applied to the coil. When there is no voltage, the COM (COMmon) connector is connected to the NC (Normal Connected) connector.
When the coil is activated with voltage, the magnet actually moves the COM connector. The COM connector is disconnected from the NC and is connected to the NO (Normally Open) connector.
So depending on what you are trying to do, you can open a circuit with the voltage or close a circuit or both.
By the way, this is called SPDT (Single Pole Double Throw). The particular relay I am using has two sets of contacts, so is a DPDT (Double Pole Double Throw) but I am only using one set for this application.
The second drawing shows an important feature of a relay labeled “Isolation.” What that means is the coil is completely electrically and physically isolated from the contacts.
Specifications: The specifications for relays are divided into the input (coil) side and the output (contacts) side.
On the input side, the voltage and current are important.
On the output side, the current capacity is the most important.
A transistor is an electronic amplifier with three leads. See picture. There are two types of transistors, NPN and PNP. I will only be using NPN. Basically a little current between the base and emitter controls (amplifies) a lot of current between the collector and emitter.