LED Circuit Lighting Troubleshooting

[mrawson]

Hi,

I am working on a controls circuit with LEDs, switches and a small fan powered by a 9V battery. The circuit is using a a breadboard for connections and soldered wiring from the switches back to the breadboard. I am using a 9V battery and using the full power for the fan portion of the circuit, with no problem running the fan. The LEDs are to be wired in parallel for a total of eight LEDs. I am wiring in parallel for individual operation. Four of these LEDs have the concave button with microswitch for a SPDT switch. The remaining four LEDs have a simple SPST switch. The problem I am running into is that not all of the LEDs are lighting up. I can turn on all LEDs individually but cannot light up all of them at once. I believe it is more of a wiring problem instead of power but I could be wrong. In some cases, two LEDs will light but the third switch will override the previous two which is odd.

Below is a circuit schematic of what I am trying to achieve with the wiring at the breadboard.

Control Board Circuit.pdf (56.3 KB)

Hopefully this description helps explain what I am trying to achieve and that you are able to help troubleshoot a little bit. A poor mechanical engineer here who only got through circuits one almost 8 years ago. We are trying to make this control board for my nephew for the holidays so troubleshooting the circuit would be ideal. If not the little guy won’t know at least haha.

Thanks!

[TS-Brandon]

Typical 9V batteries are rated for ~500mA with a suggested discharge of ~15mA. A typical 10mm LED will pull 10-20mA of forward current. If some, but not all, LEDS are lighting up then it could certainly be a power issue. I would suggest trying to power with a regulated power supply that you can monitor the voltage level and current pull. You could try running 2 9V batteries in parallel but the discharge rate might still be an issue.

[TS-Chris]

Also, you need one resistor per LED. When you only use a single resistor you end up capping the power supply voltage for all the LEDs at whatever the lowest forward voltage LED you have connected.

For example, if you light up a red LED with a forward voltage of 2 volts, that caps the supply voltage for all the remaining LEDs and you might have a blue LED that needs a minimum of 3 volts to light you’re also trying to illuminate. Since only 2 volts is available, the blue LED won’t light up.

Your SPDT switches are creating a short circuit when the LED is not selected. Don’t connect the third terminal to ground.

Try this instead: