LED sequencer

[elfumador]

Hey guys I need some help in trying to get an idea of what type of circuit I need, what I want to do is to have my gauges on my car to turn on in steps, I 'm converting all the lights in their to LED's but what I want is to have the LED's for the Gauge needles to come on first then a second after that the Gas and Temp gauges, second after that the Tach and speedometer. I don't need it to drive the LED's, Cause I'm planning to use relays to supply power to the LED's.

 

[nsklavos]

You could use a serial in/parallel out shift register such as a 74LS164 type to drive a transistor/relay circuit. Check out it's datasheet for operation.

 

[musthave]

how many led (relay)will you have to sequence .
a 4017 as 10 output you will find many circuit for those and diferent sequences .do a google search 4017 and you will find what your looking for.

 

[elfumador]

Hey thanks for the help, I'll try both just to see which one is better for my applications.

 

[philba]

The shift reg approach has the benefit of "latching" while the 4017 doesn't. Of course the 4017 can run at 12V, the 74xx164 runs at 5V, needing a regulator. Maybe a 4094 SR would do the job instead of the 4017. If you use the 4017, you will need to figure out how to keep the LEDs on, probably via a latch or flip flop.

to be clear, you will need an oscillator to drive any of these chips. the 555 timer should work OK.

I also wonder what current your LEDs will draw vs your relay coils. I suspect that it's easier (and definitely cheaper) to just drive the LEDs directly.= but that's your choice. Note that with 12V you could drive a number of LEDs in series to keep the current down.

Phil

 

[musthave]

Hi philba forgot about latching the output . what about small scr for latching would that work instead of relay.

 

[spuffock]

Nigel on holiday? No-one has advocated the use of a PIC processor. By far the best way of going about it. Say you want unequal delays? Switch them all off in reverse order? A different order? With a PIC you can do much as you like, without having to modify a load of logic . Just reprogram.

 

[Nigel Goodwin]

Nigel on holiday?

I've been running the PA for a gig my daughters band had today

My ears are still ringing!

 

[philba]

Hi philba forgot about latching the output . what about small scr for latching would that work instead of relay.

actually, the shift reg doesn't need latching. The SR inits to low. Tie the shift-in line high, as you shift, the Highs propagate down, one per clock cycle. It's always shifting in Highs. with the 4017, you need latching, as I believe I pointed out. The SCR would be an ok solution - I agree about driving the LEDs directly.

I like the CD4094 mated with a ULN2803 to directly drive the LEDs (sinking current, I believe). 3 chips, no VReg, no relays. the one question I have is will the 4094 outputs be low at power-up - it has no reset line. $2 worth of parts plus LED costs - worth a shot. If the LED current winds up more than the 2803 can handle, then the SCR would work whether latching is needed or not.

there are some nice shift regs with power output - TPIC6A596, for example, that could drive the LEDs directly but it runs on 5V logic so a VR would be needed. Kind of pricey, though.