Car improvement: automatic direction indicators

[Giuggio]

As I often drive on motorways, I always and frequently use the direction indicators in order to show the lane change. I normally did this by holding a finger down on the combination switch for some seconds for a minimum of 3 flashes, but I always felt the need of an automatic function, something that more recent cars have as standard. Something like activating the direction indicators by shortly touching the combination switch lever.

I finally decided to design a device by myself to solve the problem.

If you are fond of electronics and are capable of making a home-made PCB and circuitry, you can use the schematic diagram described in this article and connect it to your car's combination switch.

Please keep in mind that this will be on your own risk.
Any consequences that the device might have on your car are your own responsability.

Before looking at the circuit, let's see how the combination switch works for activating the indicators. The switch only uses 1 wire for both directions, and the car's electronic equipment turns the indicators on according to the amount of current flowing from pin 4 to pin 5 of the connector. Pin 4 is the power supply and pin 5 the input.
See this picture for locating the connector's pins:



For left side indicator, the current must be 25 mA. For right side, 40 mA.
The purpose of the device is to measure the current and maintaining it for some seconds by shortly touching the combination switch lever.

The circuit has therefore a measurement part by means of an op-amp LM393 and a trigger/monostable CD4538 per each side, left and right. Both parts are adjustable as for sensitivity the first part and time the second. It measures the current on pin 5 and prolong it according to the time of the monostable.
The GND, ground, can be taken from the chassis or the brown wire of the steering wheel sensor connector. Be sure that you pick up the right wire.

Fine tuning: set triggers R2 (sensitivity), R5 (time for right indicator) and R6 (time for left indicator) at middle position. Turn R2 for less/more sensitivity (left/right) and R5 + R6 for the desired time range, normally enough for 3 flashes.

WARNING: in order to connect the 3 wires to the combination switch you have to remove the steering wheel and the
airbag. Follow carefully instrucions offered by Lofty on his website at Bert Rowe's-Mercedes-Benz 'A'-class info. Removing the Steering Wheel & Related Components. Special Note Avoid accidents.
Disconnection and reconnection of the airbag must absolutely be done with disconnected battery, otherwise the airbag/SRS system will not function! .

Pictures: circuit schematic diagram and final result



Final result (some parts on this picture are mounted on the bottom side of PCB)




Components list:
C1 100uF 25V
C2 100uF 25V
C3 100uF 25V
C4 47nF
C5 220nF
C6 100nF
C7 3,9uF / 4,7uF 25V

D1 1N4007
D2 1N4007
D3 1N4007
D4 1N4007
D5 1N4148
D6 1N4148

Q1 NPN BC107 or equiv.
Q2 NPN BC107 or equiv.

R1 18k
R2 100k Trimmer
R3 5,6k
R4 5,6k
R5 100k Trimmer
R6 100k Trimmer
R7 5,6k
R8 5,6k
R9 560
R10 18k
R11 18k
R12 100k
R13 18k
R14 56k

U1 LM393
U2 CD4538

All resistive values are expressed in Ohm, capacitance values in Farad.

[lofty]

An excellent Mod, beyond my capability but very worthwhile if using the car a lot.
My problem wasn’t using the indicators on the motorway I use mine the same as you it was on the odd occasion finding they were still operating when they should be off. This was obviously caused by the steering angle be insufficient to turn them off automatically.
also I'm hard of hearing for some frequencies and so did not hear the clicking over the engine noise and the green visual warning is obscured by the steering wheel and large hands a lot of the time.

To overcome this problem I installed a warning devise designed for motor cyclists, whose indicators never turn off automatically (To my knowledge) having operated the indicators an alarm starts to operate after a minute or so (this time period is adjustable) if waiting at a junction for instance you can re start the timing sequence by touching the foot brake in the case of the car or hand brake in the case of the motor cyclist, if having left the junction you do not turn off or ensure it has automatically turned off in the case of the car the alarm gets louder and louder until you are prompted to switch the indicators switch off.
I find it works well and when on motorway find it very useful. although more often than not flick them off manually

Further details in respect of this unit can be seen at :- Audicator Limited

this unit is very easy to install and works well .