Chris Brown G4CLB solves a requirement for a safe mobile headset to work with his Wouxun transceiver.

 

Having installed a Wouxun quad-band transceiver in my car I found that using the supplied fist microphone was ungainly. It’s not to be recommended when true mobile either although strictly speaking its use is within the bounds of The Road Vehicle (Construction & Use) (Amendment) (No.4) Regulations 2003. However, I sought to use a hands-free option to be safe. There seems to be no commercial or proprietary headset compatible with the Wouxun kit so I had to build one from scratch.

 

Design

An internet search revealed a couple of sources for the wiring connections from the microphone/controller to the radio. The microphone includes a small loudspeaker and multiple control buttons. It appeared that placing an interface (I/F) box between the microphone and radio to pick up the microphone and PTT connections was the simplest solution. That way the speaker and control buttons would still be available on the fist microphone.

 

Circuit Description

The break out I/F simply redirects microphone and PTT lines and allows the other control lines to pass through. The electret microphone insert does require a voltage bias and coupling capacitor. The circuit diagram appears as Fig. 1 and there is a parts list in the sidebar.

 

Construction – Headset

I used a cheap pair of headphones for the headset because they provide a comfy and simple head-worn support for the boom microphone. I originally experimented with various wire headbands but they provided torture rather than comfort! The earphones are not connected – I prefer to use the speaker in the fist microphone rather than ‘isolate’ myself from external sounds while in the car. A short length (approximately 250mm) of 14swg enamelled wire (or similar) was shaped to use as the microphone boom. The electret microphone insert sits on the end and the wires run along the boom. The microphone boom/wiring are secured in black heatshrink sleeving. The boom itself is cable-tied to the headphone headband. Suitable headphones can be purchased for a few pounds by searching on line for ‘in-flight entertainment headphones’.

 

Construction – I/F box

The interface box is shown as Fig. 2. Most parts were obtained locally from Maplins, which has since sadly gone, but all parts are readily available from the usual internet auction sites. A small plastic project box houses a latching push-button for the PTT and a microphone socket together with breakout wiring and components for driving the electret microphone insert.

A plug-to-socket RJ45 extension lead simplifies connection to the fist microphone and the radio. This cable is run through the project box and cut within it to pick up the control, audio and PTT lines. Note that some lines are cut and isolated, some are just routed straight through and some are ‘tee-ed’ off. Double check all connections before powering up to protect your microphone and radio! Internal connections were heatshrink sleeved for insulation and protection. The existing fist microphone is plugged into the I/F box socket and the free plug out of the I/F is plugged into the radio.

 

Summary

In use the headset has proved a convenient method of maintaining comms while underway. Audio quality has been commented upon as ‘good and balanced’. The two prototypes both worked first time and the speaker-microphone control buttons are still handily available for channel changing, volume control and so on. Upon reflection, a longer RJ45 lead would have made construction a little easier and mounting more flexible in the car. Please take care that the kit, including your mobile radio, is mounted securely and safely so as not to impede your control of the car when driving. The photos, Figs. 3 and 4, show the completed unit and as I have it fitted in my car.

 

Parts List

Black plastic project box 70 x 120 x 40mm approx. To suit your vehicle.

CAB1 RJ45 M/F cable assembly 300m (see text).

M1 electret microphone insert two-pin 10 x 4mm.

C1 100µF@25V electrolytic.

R1 47kΩ 1/4W.

SW1 Latching min. push button 15mm dia.

HS1 Headset – modified stereo headphones (see text)

Hook up wire 7/0.2 as req’d.

14swg enamelled wire 250mm approx.

Heatshrink sleeve 10mm dia. as req’d.

Heatshrink sleeve 3mm dia. as req’d.