Sporadic Fan

[rthuey]

looking for suggestions on circuit to make a 5v fan to sporadically turn off and then back on continually.

 

[dr pepper]

Is this some sort of fault generator?

You could do that with a microcontroller, or possibly a 555 and a shift register random number generator and just tap off one of the bits and use that to switch a tranny that controls the fan.

 

[alec_t]

Something based on this perhaps?

 

[rthuey]

Is this some sort of fault generator?

You could do that with a microcontroller, or possibly a 555 and a shift register random number generator and just tap off one of the bits and use that to switch a tranny that controls the fan.

no it is not a fault generator.


@alec_t where is the voltage supplied on your circuit? i built it on a simulator, iCircuit, and it shows it works and has a out of 5v. i never told it on the simulator how much voltage it was using and/or where it was coming from.

 

[alec_t]

The simulator I use is LTspice. The supply voltage is implicit for logic circuits. It assumes a 5V logic supply unless you tell it otherwise (by right-clicking each logic gate and adjusting the Vdd value). Looks like your simulator is doing the same. For a real-world circuit the CD40106 IC would need a supply voltage, of course.
Edit: BTW the 'out' point on my schematic would be used to drive (via a suitable resistor) the base or gate of a bipolar transistor or FET to switch the fan on/off. If you want longer/shorter times adjust the capacitor values accordingly. For randomness it is important that the time constants of the four oscillators are not simple multiples of each other.

 

[rthuey]

Something based on this perhaps?
View attachment 69565

i purchased these and built the circuit. https://www.mouser.com/Search/Produ...tualkey66100000virtualkey661-EKZE100ETC101ME1 it does not work. i now see that they are rated at 10v not 5v.

i can not find but one 4v 100uf capacitor. not so sure of the package type though https://www.mouser.com/ProductDetail/AVX/LD104D107MAB2A/?qs=85rsz3mMAQl8LEXc8IAhEA== not sure as in whether or not i would be able to use them easily

the next ones up from 4v are 6.3v. none rated at 5v specifically

 

[alec_t]

it does not work

What supply voltage are you using? (The IC can handle from 3V to 15V.)
The electrolytic capacitors should have a working voltage at least 25% greater than the supply voltage. So for a 5V supply 6.3V rating is rather too low. 4V is definitely too low. Look for 10V, or 12V, or 16V rated caps.
How have you connected the 'out' point to drive the fan?
Have you got a back-emf supression diode connected across the fan to protect the driver transistor?
Can you post a schematic of your complete circuit?

 

[rthuey]

my supply voltage was 9v. i was going to try to get it down to 5v but did not have a 47ohm resistor. which now reminds me i was suppose to stop at radio shack last night and did not.
i had the red lead of the fan on the lead marked out in the above diagram. I do not have a diode of any type anywhere on the circuit. As for the schematic i was using the one above. which actually looks like you had supplied. thanks by the way. so the only thing i added that is not on there is the fan.

 

[alec_t]

i had the red lead of the fan on the lead marked out in the above diagram

That's why it doesn't work. A CMOS IC is unable to drive heavy current loads (e.g. a fan) directly. Also, a little 9V battery won't power a fan for very long. As I said in post #5, you use a transistor to drive the fan. The 'out' point drives the transistor. How much current does your fan draw (or what is its power rating)? The fan label should tell you. If we know that we can design a transistor driver for it.
How did you arrive at a value of 47 Ohm for a resistor (presumably intended to drop the supply voltage)?

 

[rthuey]

the battery is temporary. not sure if i want this ac or usb powered in the end. leaning towards usb since there are many ac to usb bricks available. i had forgot about post 5. fan is dc5v and .28 amps. google search gave me the 47 ohm resistor value. yes for a voltage drop.

 

[alec_t]

Try using the 'out' signal from my posted circuit as the control input of this suggested driver:-

 

[rthuey]

Curious why you chose the IRLML6344. I could only find in a SOIC package and not finding something similar. Was going to ask and i can see by looking at your location you are not in the U.S. Perhaps they are more common in your neck of the woods.

 

[alec_t]

Curious why you chose the IRLML6344

Simply because I have a Spice model for it to check the design by simulation . Almost any logic-level N-FET with a low (<0.5 Ohm) Rds will do.