I studied electronics 13 years ago and haven't done it since. I have a schematic below which I know is wrong I just don't know how to make it right. I am also hoping you fine peeps can tell me what each components value should be. This is a once off project and would take days to figure it out by myself.
The purpose is to run a fan from 10-60 seconds once power is applied then stop. I would also like to be able to vary the speed of the fan. The fan is a small 80mm computer case type fan. Not sure what the current draw is but can test if needed.
I know the problem with my schematic is the fan will be off until the RC turns on the base so I've actually created the opposite of what I need. I also am guessing VR1 would be better at the base of the transister?
**broken link removed**
I am a noob and this is my first post. Your help would be hugely appreciated. Many thanks.
I read up on your comment and thats exactly what I need. Well done.
I have a revised schematic below. I dont see how the motor can be variably controlled though.
I have added the values in I believe are required for the components but I am not at all confident. The formula of t=RC seemed a little too easy. Never have the words "use it or lose it" been so true.
I have added R1 so there is a minumum of 10s and with VR1 at full resistance will give 60s. R2 is based on a 63% charge of the RC circuit and to supply 100mA at the base of the transistor. I read 63% was the value to use so I have. Let me know if it's wrong.