# Alternating lights from a 9v battery

#### bob987

I am trying to take two lights and usign a 9v battery switch between the LED's. My thought was if i could get a square wave to go from positive to negative, since the LED's are polarity sensative I could just put them in parallel with the positive of one and the negative of the other being fed into from the osccillator. If anyone has a better Idea on how I could achieve the same effect it would be appreciated. or how I could achieve that affect, so far i can make a square wave that is only positive.

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#### KingNothing

Hey buddy, welcome to PF. I posted in your other thread, and as I said there, the most practical solution is to use a microcontroller. Most microcontrollers can power LED's directly.

#### sophiecentaur

Gold Member
Boy. A WHOLE microcontroller to flash some LEDs. What's wrong with a single squarewave oscillator. Put the diodes in series, across the supply (with suitable resistors). If you connect the oscillator (buffered, perhaps) output to the mid point (half volts) of the LED 'chain', then, when it's high, one will be lit and , when it's low, the other will be lit. Not even a dozen components involved and all of them cheap.

#### bob987

hoever, I only have a single 9v dc source. wouldn't I need negative voltages from the oscillator to switch between the diodes?

#### sophiecentaur

Gold Member
Imagine you had a (two position) switch that connected the mid point of the chain either to +9V or 0V. By moving the switch from one position to the other, the 'upper' or 'lower' LED would be lit. Your switch is shorting out one or other of the LEDs. The other one would have current flowing through it. For 'Switch' read 'amplifier output'.

+ supply -- resistor ---diode>---amp output ----- diode> ---- resistor------Ground

Does that help?

#### Averagesupernova

Gold Member
Boy. A WHOLE microcontroller to flash some LEDs. What's wrong with a single squarewave oscillator. Put the diodes in series, across the supply (with suitable resistors). If you connect the oscillator (buffered, perhaps) output to the mid point (half volts) of the LED 'chain', then, when it's high, one will be lit and , when it's low, the other will be lit. Not even a dozen components involved and all of them cheap.
Finally someone who sees things my way. It seems the tasks get simpler and simpler that people are willing to throw a microcontroller at.

#### sophiecentaur

Gold Member
Your attitude, Average-sn, would put sledgehammer manufacturers out of business at Christmas nutcracking time. :-)

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