I’ve been wanting to do this ever since the kids grew old enough to not need a baby monitor. It’s simple, quick to implement and it worked first time for me with out any major design work. But please, don’t tell my wife because she’ll kill me if she found out. What am I talking about..?
My DIY Audio Sender using a baby monitor.
DIY Audio sender
What Does it Do?
If you’re like me, you will have a nice corner that you call your own, your workshop, daddy’s home. But for me this is halfway down the garden in my work shop that I have nick named the ‘Office’. Because it is remote, my creature comforts have to either come with me or not come at all. Now as my work mates know, I love my music and I love my DAB radio but I am not going to take my radio to my ‘office’ where it is likely to get damaged. So instead. I send the music to the ‘office’ via a baby monitor.
How Did I Do It?
OK this is a quickie so don’t expect a whole lot of detail or explainations, just enjoy the ride.
Babt Monitor Set
First step, acquire a baby monitor set. You need atleast 1 transmitter and 1 reciever working on the same channel (they normally come in pairs). As the box says, this is Philips baby monitor but I don’t think he wants it back.
Locate and open transmitter.
Locate and open the transmitter. This may be referred to as the ‘Sender’ by the manufacturer.
Locate and cut the microphone wires.
Locate and cut the microphone wires ensuring there is a fair amount of wire still attached to the PCB. If the wires are too short, then just attach another piece to the PCB. This is for the audio input.
Potentiometer
Get yourself a logarithmic potentiometer of maybe 5K, this will be the input level control. Then solder 2 off IN4148 signal diodes between the wiper and one end of the potentiometer. The diodes need to be facing in opposite directions to each other. What this does is it clamps the voltage across them to about 0.7V. This will help prevent overloads on the input of the transmitter.
Isolation resistors
Get some two core screened cable, strip it back, twist and tin the screen then add a 120 ohm resistor to the end of each of the signal cables. The resistors are to help isolate the left and the right signals preventing potential short circuits when the signals are out of phase. Make a hole in the transmitter’s casing big enough to feed the two core cable through and feed the cable in stripped end first.
Connect the cables
Solder the two free ends of the resistors together then solder this to the free end of the potentiometer. Twist the screen and the return wire for the microphone together then solder to the other end of the potentiometer. Solder the microphones signal cable to the wiper of the potentiometer. Make a hole in the transmitter’s case and fix the potentiometer in place.
DIY Audio Sender Complete
Fix it all back together and your ready to go. Connect power, plug the transmitter into an audio source. Use the potentiometer to adjust the input level. Go to another room that is within range of the baby monitor. Switch on power, hear the sound.