| Electronics > Beginners |
| series parallel circuit for kids - first KiCad sanity check and suggestions |
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| williamhamilton:
Hi all, this is my first attempt at KiCad and first design to be made PCB. The design is for local school kids to solder up and be taught about series, parallel, polarity, resistance etc. Something simple but able to cover some basic concepts. I have attached a schematic file for feedback if anyone is willing - be gentle :) (KiCad file not allowed so just png file now) My next step is to check footprints against parts I can source and make up the PCB layout. Off to watch more Chris G videos cheers W |
| rstofer:
Ignore most of this... I wouldn't spend the time or money to build a PCB for this. What you can learn from the circuit will be accomplished in a few minutes. That is just an opinion, choose to ignore. I would just breadboard it and maybe play around measuring volltages and currents with my DMM. Then move on... Using a pot to feed the LED is a recipe for disaster. When you turn the knob toward the top of the drawing, the resistance declines and the LED current begins to increase rapidly. Unfortunately, an LED is not a linear load and once you start to flow current, it increases rapidly with increasing voltage. You can overcome this by putting a fixed 100 Ohm resistor in series with each pot. The value is too high, 50 Ohms is probably more realistic (given a 3V source), if you had but one potentiometer. Since you can have two pots in parallel both turned to 0 Ohms, you can count on the parallel 100 Ohm resistors to protect the LED. If you really want to simplify the project, calculate the resistor required to get 10 mA through the LED (dim) and use 2 of them in parallel to get 'bright' at 20 mA. Assuming an LED with a Vf of 2V at 20 mA and a source voltage of 3V, you calculate the resistor parallel resistance as (3V - 2V) / 0.02A = 50 Ohms. This is the parallel combination so each resistor would be 100 Ohms. This would give you dim (10 mA) when the first switch is closed and bright (20 mA) when both switches are closed. https://www.alliedelec.com/m/d/6355b8aba0b01578df0bb7b871ceefd7.pdf |
| Audioguru:
Doubling or halving the current in an LED does not change the brightness much. You need an exponential change in current to see bright and dim. |
| james_s:
You're gonna need at least one more resistor in series with the LED to limit the maximum current. I think I would just build a circuit like this on a solderless breadboard though. |
| williamhamilton:
Thanks for the feedback everyone. I think I have been convinced to breadboard this one and have the kids solder some other board. I originally had a bulb instead of the LED but the local electronics store said they would probably not be stocking them much longer. I will sit down and have a bit more of a play. |
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