How does this automotive circuit work/ how to wire it up?

[ELS122]

so I found this.. what I guess is a 3rd gen honda accord blinker module, I'm not sure it's that but I'm pretty sure.
there is a sticker on it but it's unreadable, all the text has rubbed off...

anyway, I don't understand how it's supposed to work... I drew up a schematic of it here:


the zener diode (ZD1) seems really confusing for what I think the circuit does... almost seems like something related with ignition for there to be a zener diode for one of the connections (for protection)
but yeah the more I look at it, the more I get confused.

maybe someone can help me understand this circuit... 

(also, connection 1 is ground in the circuit)

EDIT: TR1 is 2SC1214 not 2SC536 as in the circuit!

[ledtester]

Here's my crack at it...

Clearly the relay gets turned on if there is a high-enough voltage/current at D3 or D4.

So a high enough signal at 6 will turn on the relay via D4. I think the zener is there just to provide some input protection.

The 2SC536 looks like a general purpose NPN transistor: https://alltransistors.com/adv/pdfdatasheet_sanyo/2sa608_2sc536n.pdf

The 2SA844 looks like a general purpose PNP: https://alltransistors.com/adv/pdfdatasheet_hitachi/2sa844.pdf

As for how a signal at (2) affects the input at D3... I resorted to simulating it. Here's a graph of the OUT port (green) as (2) (blue) varies ramps up from 0 to 5V and back down again. The two are equal when (2) is < 2.5V. When (2) is > 2.5V the output drops to 0V.

The 100u capacitor is interesting... might have something to do with an RC timer.

[MarkF]

Except that R2 (the 22k resistor) doesn't go directly to ground.

So, I'm thinking that #2 must set it to flash between dim and bright.
And, #6 flash bright and off.

I just can't figure out how #4 and #5 are wired to the bulb.

[ledtester]

Except that R2 (the 22k resistor) doesn't go directly to ground.

good point!

[MarkF]

I see three different configurations with either one or two filaments:   
None of which really work?



Is the schematic correct???

[james_s]

Don't forget that turn signal flashers are required to detect a burned out bulb and flash quickly in that situation. Some of the circuitry may be to monitor lamp current and trigger the rapid flashing if it is low.

[MarkF]

Don't forget that turn signal flashers are required to detect a burned out bulb and flash quickly in that situation. Some of the circuitry may be to monitor lamp current and trigger the rapid flashing if it is low.

I think my turn signals just stay ON and don't flash if one of the bulbs are burnt out.
Good point however.

I just can't figure out how the bulbs are wired. 
It seems like there is something wrong with the schematic around the relay.
And I haven't even considered how both the front and back signals are connected. 
Or left and right sides.   
There is much missing.

[ELS122]

well if one bulb is burnt out, it flashed rapidly. and if all of them are burned out it just doesnt flash.

but I think I found the actual blinker relay... but it doesn't have any of this sensing circuitry it seems, it's just 3 pins it seems it goes to positive, the bulb, and ground.
I'm even more sure this is the blinker relay because it has "27w 4. bulbs max" on it, as well as "12.8v 85c/m" probably meaning cycles per minute.

maybe they're both in the same circuit... 
I haven't found them anywhere in the service manual but the service manual for some reason has just left out the indicator circuits...


what I find the most confusing is the relay connections.., if pin 5 gets switched to ground, then it must've been pulled high somewhere else. but then why is there some feedback from pin 4? if pin 4 is high, then the output would just stay high which would switch the relay back on.

maybe pin 4 is suposed to be some signal from the ECU hmm...

maybe it is a slow oscillator but not for the indicators.

if I simulate the circuit in LTC... I get this:







so, I'm guessing what it does is:

when pin 4 goes high, the output is high, and relay is turned on. and pin 5 is grounded.
when pin 4 goes low, after around 200mS the output goes low, and relay turns off. and pin 5 is connected to pin 4.



 

[ELS122]

I updated the schematic.
changed TR1 to the correct 2SC1214
added the prefix RADJ1 to the 10k on the left, RAD3 to the 1.2k connected to R12, and then RADJ2 paralel to R12 which is not in the circuit, there's only the prefix... this might be just because they revised some old circuit and used the same board, and thus no longer needed adjustable resistors, but maybe it might help so I added those prefixes!

[mikerj]

Could be an intermittent wiper circuit.  If pin 2 is fed by a variable resistance (or number of fixed resistors switched in by one of the control stalks) it would form a timing circuit with the 100uF cap and the threshold detector.  Pin 6 is likely connected to the windscreen washer, to make the wipers operate for a while after the washer has been operated.

[ELS122]

Could be an intermittent wiper circuit.  If pin 2 is fed by a variable resistance (or number of fixed resistors switched in by one of the control stalks) it would form a timing circuit with the 100uF cap and the threshold detector.  Pin 6 is likely connected to the windscreen washer, to make the wipers operate for a while after the washer has been operated.

I thought of that before... but scrolled past when I saw the the illustrated box was diffrent, and also there seemed to be 7 pins not 6...
but now I went back.. and yeah the circuit is pretty much the same, as seen here:




so it is a wiper module, thanks for the help!

[JustMeHere]

Don't forget that turn signal flashers are required to detect a burned out bulb and flash quickly in that situation. Some of the circuitry may be to monitor lamp current and trigger the rapid flashing if it is low.

I don't think it's "required".  It happens because there's the burned out bulb changes the timing of the oscillator circuit.

https://www.sunautoservice.com/flickering-car-lights/#:~:text=Why%20Does%20My%20Turn%20Signal,indicates%20a%20bulb%20is%20out.&text=Turn%20signals%20operate%20at%20a,by%20flashing%20and%20clicking%20faster.

[richard.cs]

I don't think it's "required".  It happens because there's the burned out bulb changes the timing of the oscillator circuit.

Historically it was incidental, thermal flashers (common until maybe the late 1970s?) slow down with less load or stop flashing completely. Modern ones definitely do a detection and a deliberate behaviour change, but I am not sure what the actual requirements are. They often also disable that detection in hazards mode (so it works normally however many lamps you've smashed). One I took apart had a very fancy relay with a low impedance coil that did the detection, but I'm sure recent ones do it electronically.