ljcox said:Here is an electronic option that occured to me last night.
ljcox said:Here is an electronic option that occured to me last night.
It assumes that the bike has a negative gnd. If not, then NPN transistors would be required.
It also needs incadescent flasher lamps at the front to provide a path for the transistor base currents.
When the brake is applied, Q2 turns on via R2 & the left front flasher and Q4 turns on via R4 & the Right front flasher. Thus all three lamps glow
If say the left flasher is switched on while the brakes are on, Q2 is turned off while the flashing voltage is on, thus the left lamp flashes.
If say the left flasher is selected without the brakes, Q1 is turned on via R1 & the Centre lamp when the flasher voltage is on.
Thanks Torben,Torben said:Neat. That's what I almost arrived at last night but I didn't quite make it. Thanks for the explanation!
When I simmed this in LTSpice, it occurred to me that the resistor values are fairly important if you don't want the brakes dimming the turn signals or vise versa. For me (in the sim) 47k for R3 and 56k for R4 worked OK.
It put me in mind of the various devices I've seen which dim some indicators when others turn on.
Also the sim didn't require an incandescent bulb for the flasher--I'll have to try this in real life, but in the interim, is this something which could be explained by sim/real world differences?
Thanks again,
Torben
See my rersponse to Torben above. I need to know whether the lamps are incandescent or LED.buzzardman said:This design looks perfect for what I need. I am going to give it a try.
ljcox said:Thanks Torben,
However, the circuit is only an outline.
The alternator in cars (and I asume bikes have them also) produce voltage spikes. Some years ago, an expert in auto electrics stated in this forum that the spikes can be as high as 150 Volt. So they will destroy unprotected transistors, ICs, etc.
Therefore, my circuit needs transistors that can with stand a Vce of at least 150 Volt and the base - emitter junctions would need diodes across them (cathode to E, anode to B).
I did not specify the resistors as I don't know what current the lamps take.
I need to know the cold resistance of the lamps as the transistors must be in saturation or close to it even when the lamp filaments are cold.
I would have thought that all of the resistors would be of the same value.
I suggested that the lamps need to be incadescent since the base currents go through them. I don't think there will be enough base current if they are LEDs.
What transistor did you use in the simulation?
Torben,Torben said:I was just using either the generic LTSpice PNP model or the 3906 (tried with both with the same results). However, all the indicators in my sim were generic LEDs with 220 ohm resistors in series, which probably explains the base resistor issues. I'll try later with lamps, and if I get a chance I'll breadboard it and see what I can come up with.
I'll also see if I can't get some time to sit down with my books and a pencil and give myself a good lesson on what's really going on with all this.
I mostly was interested in the switching topology to start with--but of course one thing always leads to more things to learn.
Torben
ljcox said:Torben,
I'm not sure if you saw the edits that I did to my post since you came on line while I was editing and, according to your profile, you were reading this thread.
I'll be interested to hear if you actually build one. I don't have the time at the moment.
ljcox said:I would have thought that all of the resistors would be of the same value.
I suggested that the lamps need to be incandescent since the base currents go through them. I don't think there will be enough base current if they are LEDs.
ljcox said:Torben,
That's interesting.
For the LED case, we could connect resistors in parallel with them in order to provide a path for the base currents.
And in the LED case, there won't be the cold current issue so the base resistors could be higher.
For example, say the resistors had to be 2k. Then we could connect 470 in parallel with the LEDs and the R1 ~ R4 resistors could be 1k5.
As you can see by the questions, I'm a bit confused. (not unusual)Torben said:Hi Len,
OK, I built the thing. I didn't really get what you were on about above until I did--not your fault; I just needed to see it in action. The sim is nice but doesn't really help explain it. Getting the build wrong a few times, thinking about it, etc., helped.
I couldn't get the base current to shut off the flasher LED when the brake and flasher were both HIGH until I added a resistor to ground from the Left brake line input. Do you mean the left flasher input? If I'm doing this right, that means this resistor is dissipating 120nA Do you mean nA or mA or do you mean nW or mW? when the left flasher is on. Seems acceptable.
I haven't tried driving a front flasher from it yet though, and this circuit on the board is just a very simple exploration: 2 PNPs, 5 resistors, and some wire.
Anyway, thanks very much for the patient explanation. I think I'm getting what's going on in the circuit now. Perhaps I'll build one for a high brake/flasher on my truck canopy. Someday. I won't be using 3906s though.
Torben
[Edit: nb: This was an all-LED build, one LED per side. Just to check the basic idea before proceeding.]
[Edit 2: I added 2 more LEDs per side. These are all normal 20mA garden-variety red LEDs. It works fine as long as the voltage doesn't sag. At all.]
ljcox said:As you can see by the questions, I'm a bit confused. (not unusual)
It would help if you could post a diagram.
I expect that the 100k resistor is necessary for the simulation, ie. the software can't analyse the circuit without it.Torben said:Hi Len,
I couldn't get the base current What I think you mean is that you could not switch Q1 off. This needs the base - emitter voltage to be < 0.5 Volt. The base current is virtually zero when the transistor is off. to shut off the flasher LED when the brake and flasher were both HIGH until I added a resistor to ground from the Left flasher line input. If I'm doing this right, that means that the current through this resistor is 120uA when the left flasher is on. Seems acceptable. Yes. See comments below.
Torben
ljcox said:I've revised your previous post (partially quoted below) in the light of your latest.
torben said:Hi Len,
I couldn't get the base current What I think you mean is that you could not switch Q1 off. This needs the base - emitter voltage to be < 0.5 Volt. The base current is virtually zero when the transistor is off. to shut off the flasher LED when the brake and flasher were both HIGH until I added a resistor to ground from the Left flasher line input. If I'm doing this right, that means that the current through this resistor is 120uA when the left flasher is on. Seems acceptable. Yes. See comments below.
Torben
ljcox said:I expect that the 100k resistor is necessary for the simulation, ie. the software can't analyse the circuit without it.
In the sim case, the voltage source driving the F line goes from low to high. When it is low, the F line is at 0 Volt. But in the real case, I assume that the F line is going from open to High (as I said above) hence there is no path for the current when it is open.Torben said:Actually, it works fine in the sim without the resistor, but in real life it needed the resistor there to cause the transistor to block the current to the flasher LED when the flasher line went high. I assume you mean the case where both the brake and flasher lines are high. If the F is high and the B is low, the flasher LED should glow. Otherwise, when the brake line was high both LEDs would light up (as they should), but when the flasher line would then go high, the flasher LED would not turn all the way off. This does not make sense to me. When the F line is high, the resistor should have no effect. It is only has an effect when the F line is low - since it tends to pull the line low if the F line is (without the resistor) going from open to High. With the 100k grounding resistor there, it worked perfectly.
Not sure why, but the sim doesn't seem to care whether it's there or not. See below.
Torben
ljcox said:I still can't make any sense of it. So I've drawn the attachement.
Please measure the voltages (without the 100 k resistor) at the C, B & E of both transistors for each case.
A point that just occurred to me is the that EB junctions will go into Zener breakdown if the supply is 12 Volt. And it may occur at 6 Volt.
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