I've put together a Vellman MK102 kit (Flashing LEDs) to try and get a handle on how circuit work.
I wondered why resistors where placed after the LEDs, and I learned that it's because resistors affect the overall current flow throughout the whole board (electricity being like a chain link rather than flowing like water through a pipe).
My board has both 1K and 10K resistor. How does that work? If electricity is resisted by 1K throughout the whole board how does it go up to 10K? Which has precedence and why are there two types of resistor in the board?
Can somebody explain to me how having 1K and 10K resistors in the same circuit works?
Best Answer
electricity is resisted to 1K throughout the whole board
Not the whole board - just all the way through a particular path. Both water and the chain belt work as metaphors, but we're not used to chains splitting and recombining.
Recall that electricity flows in a complete circuit: a loop through the power source.
There are multiple complete circuits that current can take through the board, for example:
That path goes through the LED, resistor, and transistor. How much current flows depends on how "on" the transistor is. The resistor is there to limit current when the transistor is "fully on".
Compare:
The blue path goes through the variable resistor, which has a 10k resistor in series with it so behaving like a variable resistor from 10k to 260k. It also goes through the base of the transistor, tending to turn it on.
In both cases the resistors limit the current - to different values of current.
The actual operation depends on variable current flow in the capacitors as the transistors turn on and off; the easiest way to do this is to put it into a simulator like Falstad and watch the result. Astable multivibrator in Falstad. That example uses different values and so oscillates at a different frequency. Try varying them.