Detailed Instructions for Wireless Microphone Kit

This is a common kit available from suppliers on eBay. It is an excellent project for teach soldering skills and the concept of wireless communications. Like most of these kits, there is very little documentation. In fact, this kit came with a sheet of paper totally in Chinese. Interesting, but not really useful. We bought a large number of these kits for Maker Camp at The MakerBarn. Assembly instructions had to be written, so why not do it as an Instructable so that everyone could make use of them.

Step 1: Material and Tools

The kit is simple, only a few parts to solder.

1. 2.2K Resistor, R1 Color Code - Red, Red, Black, Brown, Brown

2. 22K Resistor, R2 Color Code -Red, Red, Black, Red, Brown

3. 220 Ohm Resistor, R3 Color Code -Red, Red, Black, Black, Brown

4. 2ea 0.1uF Disc Capacitor, C1 and C2 Marked "104"

5. 0.01uF Disc Capacitor, C3 Marked "103"

6. 3ea 30pF Disc Capacitor, C4, C6, and C7 Marked "30"

7. 10pF Disc Capacitor, C5 Makred "10"

8. Transistor, NPN type SS9018, Q

9. Coil, 4 Turns, L4T

10. Switch, K

11. Microphone, MIC

12. Battery holder for CR2032 battery.

Tools Needed

1. Solder Iron suitable for printed circuit boards

2. Solder

3. Needle Nose Pliers

4. Diagonal Cutters

Not supplied but needed:

1. CR2032 Battery

2. Length of wire, approximately 18" long, 24ga or smaller.

Step 2: Parts Location on Printed Circuit Board

The circuit board is very clearly marked with the component locations and values.

Start by installing R1, R2, and R3 in their proper locations. If you have any doubt in the color codes, use an Ohm Meter (Digital Multimeter) to verify values.

Step 3: Soldering Resistors

After inserting the resistor, pull them snug against the PCB and spread the leads a bit to hold the resistor in place. Solder the resistors and trim with the diagonal cutters.

Step 4: Install and Solder the Disc Capacitors

The capacitor values are marked with a number. Install the capacitors in the PCB. Solder the capacitor leads and trim. The solder side of the board should look much like the photo.

Step 5: Install the Transistor

Install the transistor in its location. Be sure the flat side of the transistor aligns with the flat marked on the PCB. Press the transistor down until it is about 3mm above the PCB. Pressing further may break a lead or damage the transistor. Solder and trim.

Step 6: Install the Battery Holder and Switch

The battery holder should snap into place.

Insert the switch into its location and bend the leads as shown in the photo. This helps hold the switch in place while soldering. No need to trim these parts.

Step 7: Install the Microphone

Examine the bottom of the microphone. One lead has connections that extend out to the case. This is the ground side the other lead is the PLUS. Insert the Microphone into the MIC location with the PLUS lead in the hole marked with the +. Do not force the Microphone all the way down, allow enough lead length for adjustment of the microphone. Solder and trim.

Step 8: Prepare and Install the Coil (Inductor)

Carefully scrape the enamel off the leads of the coil. Be careful to avoid distorting or crushing the coil. When bare copper is seen all around the lead, tin the lead with a bit of solder. the tinning is a good way to insure the copper was clean. Insert the coil, solder and trim.

Step 9: Your Wireless MIC Is Now Finished

The antenna wire is not strictly needed, but it improves the range quite a bit. solder on end of a wire into the hole marked "TX". Experiment with the wire length, eighteen inches is a good starting point.

Insert a CR2032 Lithium battery into the holder. Turn on the power switch.

The wireless mic operates in the low end of the FM band, around 88MHz. The radio should try to "lock" to the carrier when tuning across the lower band. Tap the mic, you should be able be able to hear it in the radio. You can change the frequency of the transmitter by spreading the coil a bit. Spreading the winding raises the frequency.

You won't be using this transmitter to go into the FM broadcast business, but it's fun to witness the magic of wireless communications.