I built this kit last night, and tapped the input across one of my speakers.
formatting link
It's their standard one channel light organ designed to work with low voltage lamps.
It worked, but I had to crank the speaker really high to get the lamp to flash. Looking at the circuit it seems that all I need to do is find a way to flash one side of the optisolator to make it work. At the moment it's using the power from the audio amplifier to do this, but could I add a transistor from the 12v supply, connect this to the OI input and feed in a lower power signal to do the switching?
Ideally I would like to run this from an audio line level signal, not the speaker output of my amp.
I was looking at the schematic again - do you think that the pin 6 on the OI could be wired up to do the job? It seems to provide an electrical input to trigger the switching .
Maybe breaking the connections on pin 1 , connecting this to pin 6. Then breaking pin 2 and connecting this to GND.
Obviously at this point I would never want to wire it up to a speaker again, but maybe the half rectified line level signal would be enough.
I'm great with theory, just no so good with number crunching.
You would lose the isolation if you did that. R10 and RV1 determine LED current, experiment with the series resistance to the LED and you can probably use the circuit as is. You may try driving the LED directly without RV1 using R10. Careful not to overdrive the LED.
You could try a hefty capacitor between RV1 and the parallel combination of the shunt diode and optocoupler diode, this would act as a voltage doubler as far as the opto coupler diode is concerned because the shunt diode would cause the capacitor to charge to the peak input voltage, then on the opposite half cycle the voltage on the capacitor is added to that of the incoming signal. Whether that's enough to run off a line signal is another matter, you may have to put a couple of transistors in a gain stage in front of the opto - is there some safety reason why you need to use the opto?
No I don't reallly need the opto - the line level signal is 'safe' - that's why I was thinking about using the transistor in the OI - if I understand the pin out, then pin 6 is an electrical 'base'.
"Kasterborus" schreef in bericht news: snipped-for-privacy@k37g2000hsf.googlegroups.com...
That opto-coupler is required to insulate the speaker output from the lamps and their power supply. I'd leave it that way. Make an error and you blow your amplifier.
At the same time that opto coupler causes your problem. It's input LED uses to function at 0.8-1.2V and some mA of current. At normal speaker output levels the LED will hard produce any light. That's why the output of that optocoupler is ampified so hard.
Increasing the volume makes sense but you've already found out that you have a lot of sound at about 2Vpp already. Besides, you introduce some distorsion as the diodes (the LED and the 1N4148) are a highly non-linear load. That's one of the reasons that pretty high series resistor is added. As long as the impedance of the speaker is far below the impedance of the LED-resistor combination you'll hear not too much of it. You nevertheless will need some series resistor as you need to limit the current through that LED.
One thing you can try is getting another opto-coupler. Maybe you're lucky to find one that works better in your circuit. But you can be sure. After all, the LED is supposed to work way below its normal specs.
Another, better, way is using an input amplifier. See below.
Aan de ene kant is het een klassieke schakeling. Aan de andere kant, ik heb hem zo'n beetje uit mijn blote hoofd opgekrabbeld. Deze schakeling wordt geacht een keer of tien te versterken. Belangrijker is dat er ongeveer 1mA ruststroom door de LED gaat. Wat weer tot gevolg kan hebben dat de versterker achter de optocoupler zwaar overstuurd wordt. Je kunt eventueel experimenteren door de 100k weerstand groter of kleiner te nemen.
(Uiteraard haal je de 12V voeding uit de versterker en niet uit die van de lampen.)
Some optos have no external connection to the base of the phototransistor but its easy to check if you have a DMM with a diode check function - each of the E/B & C/B junction tests as a diode.
You could replace R1 with a 47k pot from Vcc to GND with R2 to the wiper - adjust so its just on the switching point, feed the line signal to T1 base via a DC blocking capacitor - say about 0.22 or 0.47uF.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.