Light pulse then on

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nzgrub

New Member
Newbie to electronics, but love to learn.
12vdc circuit. I want when power is applied to circuit the output will be a light that pulses 5 times in about 3 seconds (adjustable would be nice) then stays on until power switched off.
I have available a 555 timer and a 4017 Decade Counter. Which I think should be suitable.
If someone could help with a circuit diagram that would be much appreciated.
Thank you.
 
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The easiest way (as with most things) would be to use a micro-controller - an 8 pin PIC and a small regulator is all that would be required. However, probably the easiest solution would be an Arduino Nano, and the programming would be VERY simple to do (they even come pre-programmed with a flashing LED program installed, which could very easily be modified to do what you wish).
 
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Last January there was an opposite request on a different site. Someone wanted a 555 circuit that had a delay at power-on, then started flashing.

Yours can be done with one 555, or one quad Schmitt trigger NAND gate such as the CD4093 plus an output transistor to drive the LED.

Start with the basic 555 astable circuit, with the LED connected so it is on when the 555 output is low. To this, add an R-C circuit to the Reset input. Reset will be held high while the capacitor charges down from Vcc to GND through the resistor. During this time, the output is flashing. Eventually, the Reset input will be low enough to reset the chip, forcing the output to stay low and the LED to stay on.

Here is a first pass at a schematic. All component values are approximate, so feel free to adjust to match your inventory. The circuit is from the datasheet for the CMOS version of the 555. It has the design equation.

If you are using a bipolar 555 (NE555, LM555, etc.), increase C1 and C2 to something in the 10 to 47 uF range. This reduces the values for R1 and R2 to be within the recommended range for the bipolar part.

ak

 
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Use mBlock to program a Arduino Nano board or ATTINY85 (I think this will work) :



Something like this -


Use an Arduino Nano board for solution or use a Nano board to program the ATTINY micro with the
solution (code).

Note it would be easy to add another pot to control brightness using the PWM in the nano or ATTINY85.

Last if your LED is a 10 - 20 mA type of led you can eliminate the power transistor.


Regards, Dana.
 
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The implementation may be difficult if you have never tried any solution, after which it gets much easier. Realization often requires a critical review of specs. and construction options.

specs
-----
"output will be a light that pulses 5 times in about 3 seconds (adjustable would be nice) then stays on until power switched off."

LED = TBD or any colour and is normally ON then pulsed OFF after a button push, trigger, or contact closure.

It will switch OFF 5 times in approx. 3 seconds, ie. rate = 4/3 Hz to 6/3 Hz (adjustable rate or duty cycle or both? ?) or something else?

Battery or ACDC supply power options should be given.

You may need more details to decide.
 
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nzgrub said:
12vdc circuit. I want when power is applied to circuit the output will be a light that pulses 5 times in about 3 seconds (adjustable would be nice) then stays on until power switched off.
I have available a 555 timer and a 4017 Decade Counter.
Click to expand...
LTspice sim below:
It stays on at the 6th pulse.
Pot U3 adjusts the pulse frequency.
R2 and R3 set the power-on capacitor voltage to 1/3rd Vdd so that the first pulse is not longer than the rest.

What is the light?

 
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You might want to check out load dump on a motor cycle as that could easily fry your
555 timer and CD4017....

If you have a scope put it on infinite persistence, and monitor Vdd rail for parts.
See if there is any HV transients,. and use transorbs to protect.

Also set it normal persistence, aset trigger to Normal, trigger V to 555 timer limits,
and see if you get any triggers. Time base ~ 100 uS.




Regards, Dana.
 
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Here is a first pass at an alternate circuit that uses a digital counter to assure an exact number of flashes. Technically, it has the same first-half-cycle delay as an uncorrected 555 circuit. However, that extra 40% of one cycle is spread out over 512 cycles, so it has no visible effect on the outcome.

R2-D2-D3-D4 form a 3-input AND gate. When U1 pins 1, 13, and 15 are high at the same time, the 4060 oscillator is disabled. This happens at the start of the 6th flash, so the output stays enabled when the oscillator freezes.

ak
 
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crutschow said:
Load dump transients are not likely to occur during brake application, and that's the only time the circuit gets power.
Click to expand...

Depending on the bike many motorcycle electrical systems are HORRIBLY crude, often just a rectifier fed from a permanent magnet alternator. Regardless, motorbike or car, it needs a regulator and input protection as well - or it's very likely to have a short live.

However, I'm VERY, VERY sceptical about the legality of such a brakelight, it would certainly be illegal in the UK.
 
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Load dump transients are not likely to occur during brake application, and that's the only time the circuit gets power.
Click to expand...

One could make a simple latching V comparator circuit and run the bike to see if a trip
occurs at elevated V. My thoughts are one has to measure to confirm "not likely to occur".

A pulsating break light interesting idea (certainly an attention getter) but could confuse
other drivers......


Regards, Dana.
 
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Nigel Goodwin said:
However, I'm VERY, VERY sceptical about the legality of such a brakelight, it would certainly be illegal in the UK.
Click to expand...
They are legal in California in the US if they flash no more than 4 times before becoming steady (I don't know if they are in any other states.).
I had one on my motorcycle to reduce the chance of a rear-ender for any following vehicle not noticing my brake-light.
 
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Here is the circuit in #14, updated and re-worked for an automotive application. The light flashes 4 times, then is on steady. Q1 can be any appropriate p-channel power MOSFET.

R1 - C1 make a power-on reset pulse for the 4060 in case its internal counter stages do not initialize correctly.

R6 provides a discharge path for C1 when the 12 V source goes open-circuit.

C3 is the power supply decoupling capacitor for U1. It should be as close to U1 as possible, with short leads.

With R3 at mid-range, the flash period should be approx. 0.6 sec (0.3 s on, 0.3 s off). This is the rate in post #1.

ak
 
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And just for grins, here is an alternate theory. This one uses one Schmitt trigger gate (U1B) as an oscillator that drives the output transistor, and another gate (U1A)as a power-on monostable that enables the oscillator for a time period equal to the desired number of flashes.

The flash rate and the number of flashes before steady are not linked as in the previous solutions based on a counter. R5 sets the flash rate and R4 sets the number of flashes. U1C and D are not used, so their inputs are terminated.

Because C1 is so large, D1 is added to protect U1A from a reverse-voltage spike that has enough energy to damage its input protection circuit.

ak

 
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