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Welcome to ETO, jithinsmmb!
The first 555 timer in the circuit simply sends the clock pulse to the CD4017 decade counter. Every time the push-button is pressed, it triggers a pulse from the 555 into the clock of the 4017. When pressed once, the first output of the 4017 is switched on. The variable resistor determines the output frequency of the second 555 timer. The first variable resistor is presumably set to a high setting, which slows down the output pulse of the second 555, which slows down the wiper motor.
When the push-button is pressed again, the first 555 sends another pulse to the 4017 and switches on the second output. The variable resistor here is probably set for a slightly lower value, which increases the frequency of the output of the second 555, speeding up the motor slightly. This entire sequence repeats for every depression of the switch.
I hope this helps!
Der Strom
The speed of a DC wiper motor is not controlled by the frequency of pulses. The speed is controlled by PWM which is completely different.
PWM adjusts the duty cycle of the pulses, not their frequency.
I don't think anything from that website in India works properly.
The speed of a DC wiper motor is not controlled by the frequency of pulses. The speed is controlled by PWM which is completely different.
PWM adjusts the duty cycle of the pulses, not their frequency.
Thanks, AG. I was just looking at the circuit and noticed that only the frequency is changed. So, are you saying this circuit wouldn't work anyway? Or am I missing something important?
It could be an intermittent wiper speed control. Meaning it operates at a very low frequency (say, 1 pulse every 30 seconds minimum to 1 pulse every 2-3 seconds maximum). Each pulse triggers a single wipe cycle.
Looking at the R and C values at the 2nd 555 and doing some math, or running the circuit in LTSpice should give an idea of what frequencies are output at each of the decade counter's levels.
It could be an intermittent wiper speed control. Meaning it operates at a very low frequency (say, 1 pulse every 30 seconds minimum to 1 pulse every 2-3 seconds maximum). Each pulse triggers a single wipe cycle.
Looking at the R and C values at the 2nd 555 and doing some math, or running the circuit in LTSpice should give an idea of what frequencies are output at each of the decade counter's levels.
I believe that is exactly what it is. IC1 the first 555 is just a one shot used to increment the 4015 decade counter/divider. I don't know why it is there other than to possibly eliminate switch bounce from the push button. On the 4017 if they wanted a count to N and recycle pin 15 the reset would go to N, it looks like they have a 10K resistor in there to ground? Pin 13 the clock enable does go to ground as I would expect. If I wanted N = 9 I would just ground pin 15? I don't get the 10 K to ground?
As the counter increments up each pin will go high as the others remain low. VR1 through VR10 determine the voltage applied to R4 which in conjunction with R5 and C3 determined the output frequency (pulse repetition time) of the second 555 IC3. The PRT determines the pulse rate to trigger the wiper motor.
Anyway, I see it as an intermittent wiper delay circuit. The top of R4 could be tied to the wiper of a pot across Vcc & ground and pretty much the same effect could be had, sans the stepping I would think.
That is a poor wiper delay. How will the motor stop with the wipers parked in the down position?
Usually a wiper motor will continue to run because of a park switch that keeps power going to the motor. When the main power is cut, it will run until it "parks" at which point the park switch finally cuts power.
A proper wiper delay only needs to send a short (say 1/2second) pulse to start the wiper. Then let it finish one cycle and park on it's own. What you need is a circuit that sends a 1/2 second pulse, and has a variable delay between Thad pulses from say 1 second to several seconds.
It could be an intermittent wiper speed control. Meaning it operates at a very low frequency (say, 1 pulse every 30 seconds minimum to 1 pulse every 2-3 seconds maximum). Each pulse triggers a single wipe cycle.
Looking at the R and C values at the 2nd 555 and doing some math, or running the circuit in LTSpice should give an idea of what frequencies are output at each of the decade counter's levels.
This makes much more sense, considering the resistor and capacitor values for the second 555. I am somewhat confused, though, about the frequency this would produce. If I did my math right, the second 555 (depending on VR1-VR10) would send pulses at at a minimum rate of 2.676 times per minute, and a maximum rate of 3.942 times per minute. This hardly seems useful for a wiper speed controller. Could someone check my math? I used the equation f=1.44/((R1+2R2)C1), with the variables referring to this picture: **broken link removed**
f is in kilohertz, R1 and R2 are in Kohms, and C1 is in uF. Perhaps I have my units wrong?
Der Strom
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