Hi dr pepper,I think this fulfills your explanation.
However your explanation may not be what your traffic lights want to do.
Here in the Uk this is not how ours work.
Hi dr pepper, the green led is fine. But when the digital input is high, and green is out, then both red and yellow light up strongly and then the red is bust: so the current -instead of being sinked through pin 3- goes straight through red and yellow led in you intial design.Thats what can happen if you design a circuit in your head without testing.
On my hand drawn circuit insert a 1k in series with the Red Led's anode, this might introduce some brightness differences, but maybe not as green Leds tend to be more efficient.
I dont know why the green Led would blow in the circuit you just showed us, there is a 1k permanently in series with it, so it should never see more than a few ma, for that matter cathode current for red has to go through R2 or R7 on your circuit, so how enough ma's gets through to blow the Led's isnt obvious to me, unless maybe the polarity reverses and that takes out the Led, though thats unlikely.
The input drives the led's fine, except that when pin 3 should be sinking the red LED, the current flows through the yellow LED.With your attached circuit, the logic input will need to be actively driven (or connected) to either 0V or the 5V supply; eg. a switch or a CMOS logic output.
An open input will give strange results from the look of the circuit.
Done. But there are a few more issues:I agree, hence the 1 k in series with red between its anode and the emitter.
Hi dr pepper, thanks for your responses! I reworked a bit the circuit, see attached schematic. Never mind the second order input filter, this is to be removed and only a capacitor on the basis is needed (I did this for additional testing for another application).1) the 555 triggers on a falling edge, Q3 is to invert this and trigger on a positive.
2) for pin 3 to go high as above pin 2 needs to momentarily go low (C1 does this)
3) hmm not sure about that one the circuit initially had 2 inputs, some of the hold on current might be comming through r6, a mosfet might work.
Oh I understand. The mosfets used are 2N7002, N-channel.Dunno.
When you say 'these' I'm not sure what you mean, theres no mention on the schem of part numbers for the fets.
Are you using 2n7000's?
I was just wondering whether you were going to use mosfets or jfets as one inverts and the other does not, but then you did specify mosfets.
Glad to see you got it working.
Interesting, I look forward to that. I have been impressed with your circuits in the past, among them this moisture sensor based on a 74HC132 oscillator, very usefull design!Late to the party. In case anyone is interested in an alternate approach, the requirements in posts #1 and #16 can be met with a single ULN2803 darlington transistor driver plus a few Rs and one C. This includes the LED drivers. The part is basically an 8 section open collector inverter, with each section rated for 50 V and 500 mA. I'll try to post the schematic later.