Flasher Circuit as LFO
The purpose of this project was to experiment with a simple flasher circuit that I ran across on the net. This circuit flashes two LEDS opposite to each other in a triangle waveform (or mostly as a triangle…more of a charging RC constant thing). The plan was to use it to drive a VCO into an XOR for a ring modulating sound. This seemed like an interesting way to get two waveforms that are opposite of each other. Is it original?..probably not. Could I make it famous…maybe with a cool name like Atari Punk Console. How about the intellivison country console?
The basic flasher circuit is as follows:
The 10k resistors control the speed. If you wanted a speed control, a double ganged pot would work. Be sure to put a 5 k resistor in series though because otherwise you might find your pot smoking if you try and get too high. (With the frequencies…too much current ya know…what..its not a drug thing!).
The 1K resistors limit the current to the diode, but also charge the caps…so anything above 3k will just stop the circuit.
Here is a flashing you tube of the circuit.
Ya…the cat trys to help me at times. Mostly by stealing resistors and hiding them throughout the house. I have asked around…this is not apparently normal behavior.
Moving on.
So, building on other experiments, it was found a while ago that a simple VCO could be fashioned with an inverter oscillator and a transistor in the feedback loop. When the transistor is switched on, it shorts the resistor, making the frequency go up. Its not a particularly stable circuit…in fact its downright squirrely. But a lot of fun.
Sample1 - This sample is at Vout. Basically the inverter is configured as an inverter. The Transisor turns on and off shorting out the pot and forcing the frequency to shift up.
Sample2 - Nothing too different here. Im touching the ground and the timing cap in the audio oscillator for some weird effects. Looks like this would make a good touch point.
Adding another oscillator adds a bit of complexity. In the diagram, there is a switch to indicate the sounds made. With the switch off, the second oscillator is just putting out a constant audio frequency. Normally, that sounds kinda plain, but when its XORd with the first signal, the sound is pretty neat.
Sample3 - Sweeping sound XORd with a constant signal.
With the switch on, you have two signals that sweep up opposite of each other.
Sample4 - Two oscillators driven by the opposite fading values.
Finally, a second LFO circuit (another Schmitt trigger oscillator) is added to modulate one of the audio oscillator. In this case, the transitor was swapped around for different sounds. With the emittor on the output side of the gate, the LFO is stable. With the emitter facing the input, the LFO does strange things. I think its because the the transisor draws from the LFO, hindering the charging process thus slowing it down.
Samples:
Sample5- A LFO oscillator drives one on the audio oscillators with a diode. Kinda giving it a beeping sound. In this case, the Transistor on the audio oscillator has the emitter facing the output of the gate. Note the LFO has a steady beep to it.
Sample6 - Same as above, but the transistor is flipped. Its kinda strange. The LFO slows down for a beep beep beeeep beeep beeeeeeeep sound.
Sample7 - Longer sample with some knob twisting.
Sample8 - led swap. In this case, I have a switch to swap out the LEDs in the flasher circuit. The LEDs that I used were from a Chirstmas tree light set. I saw a set of 40 or so lights for 5 bucks and figured it was a pretty good source for LEDs. The characteristics of the circuit are totally different with a green LED versus a red one.
Final notes. It was fun to play with, but kinda wonky. I would breadboard anything before commiting it to a circuit.