Question about resistors.

Amps = Volts/Resistor

So if the resistor is twice as resistive, then the amps is half as much.

I don't quite know what you're asking by 1-20 V dc "current". I think you mean that the sound activates with any voltage from 1 to 20 Volts applied. If you put a twice the value resistor in series, it may have no effect as long as the coupler gets enough operating current at 1 Volt even though the resistance is higher. And the 330 resistor may be required to prevent the current from going too high and burning out the optical coupler input. I suspect that, so don't leave it out. Could you publish the diagram?

cjack posted:

Amps = Volts/Resistor

So if the resistor is twice as resistive, then the amps is half as much.

I don't quite know what you're asking by 1-20 V dc "current". I think you mean that the sound activates with any voltage from 1 to 20 Volts applied. If you put a twice the value resistor in series, it may have no effect as long as the coupler gets enough operating current at 1 Volt even though the resistance is higher. And the 330 resistor may be required to prevent the current from going too high and burning out the optical coupler input. I suspect that, so don't leave it out. Could you publish the diagram?

Here's the diagram:  I'm trying to do the lower-right-hand one, with the optical coupler to activate it.  Also wonder about the wire hook up to the "loop" connector; it isn't clear where the other wire goes in the "MOM(?) port.  Under the board they connect to two to different traces, so I guessing one is "right" and the other is "wrong?"  The diagram says use a 460 ohm but someone here recommended a 330 instead?

Just don't want it to not activate until reaching a high voltage as that won't do.  Need the sounds to come on as soon as the table beings to turn, not wait until it is spinning at high voltage.

So the table turns faster when the voltage is raised? And you would like it to turn on at 1 vdc? One volt is too low for the opto coupler. It would be better to have a voltage of 5 to 15 volts (say 12 vdc) thru the resistor which is applied with a small relay or switch when you activate the turntable drive voltage. Is the turntable voltage applied with an on/off switch? Another pole on that switch could turn on the required coupler voltage. Then the drive voltage could be varied from 1 to 20 vdc to drive the turntable, all the while, the sound unit would be active.

It's driven by a DC power-pack with a variable throttle which regulates the voltage.  The turn table starts moving as soon as voltage is applied, so waiting for it to ramp up to 5 volts it would be going fairly fast before the sounds started, which would look/sound weird.  Be better for it to start as soon as current lights up the optical generator in the opticoupler, and limit the volts/amps  going to it so it doesn't burn out.  The sheet said 470om for their ac powered circuit, and using DC as mine does it was suggested a 330 ohm resistor be used instead, in a previous thread/posting.  Now that I have components an EE friend said "are you sure about the resistor?" ... so here I am.  Don't want to burn out the device. I have the LTV-8171 suggested here https://ogrforum.com/t...ate-turntable-sounds and am trying to get the resistor setup right for what I'm trying to do.  Also got the other optical sensor suggested .. .but haven't used it hoping the LV-8171 is a simpler solution.

I assume by "MOM" port you are referring to Momentary (as opposed to Mother ).  For your application that port can be left un-connected.  Only the 2 wires need be connected to your opto-isolator.

The challenge in YOUR specific application is triggering the sound at 1V DC.  With the hookup you are proposing, a 330 ohm resistor makes for a more sensitive trigger than a 470.  It will trip at a slightly lower voltage.  There are other issues described in the other thread with choice of power rating for this resistor but those are really secondary (easy to deal with).  Again, it's getting the thing to trip at only 1V which is the trick.  IF you already have the 470 resistor, then just hook it up and see if it works.  Use the LTV opto-isolator; it is more sensitive than the one shown in your "factory" diagram.

Do you have a link to your actual DC gearmotor?   It seems to me that the idea is to activate the sound module when the turntable actually turns.  The problem with triggering at 1V (or so) is two-fold.  First, there is variation in the detector (opto-isolator).  Second, there is variation in the DC gearmotor itself.  In the latter case the turntable load varies so maybe it takes a few tenths of a Volt more/less depending on what's on the turntable.

So is there any way to detect the gearmotor is actually turning?  Perhaps the shaft of the motor itself is available on the side opposite the gearbox; that shaft would be spinning at a good rate even for slow speed motion.  Since it appears you need to mess around at the component-level anyway, perhaps there might be an alternative that would detect what you want (motor turning) rather than just a proxy (motor voltage).

stan2004 posted:

I assume by "MOM" port you are referring to Momentary (as opposed to Mother ).  For your application that port can be left un-connected.  Only the 2 wires need be connected to your opto-isolator.

The challenge in YOUR specific application is triggering the sound at 1V DC.  With the hookup you are proposing, a 330 ohm resistor makes for a more sensitive trigger than a 470.  It will trip at a slightly lower voltage.  There are other issues described in the other thread with choice of power rating for this resistor but those are really secondary (easy to deal with).  Again, it's getting the thing to trip at only 1V which is the trick.  IF you already have the 470 resistor, then just hook it up and see if it works.  Use the LTV opto-isolator; it is more sensitive than the one shown in your "factory" diagram.

 

I have the LTV-8141 to use ...

I go to thinking that one solution would be an LM358 which will power up with a single supply (say 9 t0 12 vdc) and behave as a zero crossing detector, detecting 1 volt dc easily. The output can go to the rail voltage of 9 to 12 vdc and trigger the optical isolator. One can draw something up for this...maybe include the opto diode in the feedback loop of the opamp. One thought...

I'm not exactly familiar with what is going on in this specific instance, but does this sound about right:  You have a motor that starts turning at around 1 volt applied, and a sound board that doesn't kick on till it sees around 5 volts.  you want them both to start up at the same time with a single control.  

The simplest solution I can think of is the diode drop mentioned above.  Place several diodes in series on the input to the motor to effectively drop the voltage the motor will see.  This does have the problem that the motor's top speed will be lower as it's top voltage will be reduced by about .6 volts per diode.  

I'm not familiar at all with the sound board here, so if it actually reads the input voltage to adjust the sounds this other stuff would have to be re-thought:  

The 'correct' electronic fix here would probably be to use an op-amp comparator to detect whenever voltage is applied, and trigger a relay or transistor on and off at the 5v level needed for the sound board.  While not really a very complex circuit to build, it has it's quarks, and is probably pretty intimidating for many folk around here.  

As such there is a simpler, if slightly more expensive way to do the same job.  For about $5(or less) worth of modules shipped from china you could use an arduino clone, a relay module, and two resistors.  With these you could set the sound module to 'turn on' at any voltage you like with better than 0.1 volt sensitivity.