What type of capacitor....

[Sumner]

I use the circuit above in my Bluetooth box car....

https://1fatgmc.com/RailRoad/DCC/page-43.html

.... I going to use a similar circuit in an N scale Snow blower.  At the bottom middle is the blue tooth receiver (KCX-BE-Emitter/Receiver).  The recommended wiring for it includes a 10v/100 uF capacitor between the input voltage and ground.  The circuit has been fine without the cap with the battery power supply in the car. 

In the new application I'm going to use rectified 12V DCC current, DC stepped down to 5v with a step-down module (12v to 5v).  I think I should add the cap on the input voltage to the Bluetooth receiver.

What type of cap should I use?

Sumner

[peteski]

You should also include a capacitor to smooth out the rectified DCC voltage fed to the 12->5V module). That one should be rated for at least 20-25V.  Since DCC is a square wave with pretty much 100% duty cycle, that cap can be smallish like 100µF.  Any aluminum electrolytic or Tantalum cap should work.  I would also add a smaller ceramic cap (like 0.1µF) to deal with the higher frequency spikes on the DCC signal.  I actually don't think you will need any large caps on the 5V side of the module, but I would also add a 0.1µF cap there instead.

[Sumner]

Thanks, that is what I needed to know. 



Does the above look OK.

Sumner

[Sumner]

I have 100 microfarad 16 volt. I have 47 microfarad at 25 volts. Could I use two of the 47 microfarad to replace the 100 microfarad cap?

Sumner

[ednadolski]

[peteski]

I have 100 microfarad 16 volt. I have 47 microfarad at 25 volts. Could I use two of the 47 microfarad to replace the 100 microfarad cap?

Sumner

Yes, that will give you 94µF - should work.  But the 0.1µF does not go on the DCC voltage side. I was recommending it to also be connected on the DC output form the rectifier (in parallel with the 100µF cap).  Basically the small value ceramic caps are better for handling high frequency noise or fast voltages spikes which can be present on the track powered with a DCC signal. It might not be needed, but it is a cheap insurance.

Actually looking at the circuit again, you are powering the audio amp from the rectified DCC voltage.  If you hear some unwanted sounds from the speaker you might have to use cap larger than that 94µF. 

Peteski

[Sumner]

...But the 0.1µF does not go on the DCC voltage side. I was recommending it to also be connected on the DC output form the rectifier (in parallel with the 100µF cap).  Basically the small value ceramic caps are better for handling high frequency noise or fast voltages spikes which can be present on the track powered with a DCC signal. ........Peteski

Thanks, updated the wiring.

I'm going to use one of the LokPilot Nano Standard's that I bought cheap last year (think you did also).  Have you used any of yours?

There are 4 solder pads on the back side marked, Common (+pole), Output AUX1, Output  AUX2 (violet) and GND.  I plan on using the motor leads for the snow plow motor.  That leaves 2-3 LED light outputs and the audio amp (which I believe draws 63ma, the Bluetooth receiver 35ma).  I guess I could power them off of one of the AUX outputs but what about powering them using the common (blue) and that GND pad?

The motor draws 35ma at 12 volts (tested it with amp meter).  So the Bluetooth and amp might be about 100ma.  Everything should be well under 1 amp (rated for that) and all the LED outputs are very small.  So question is could I power the amp and Bluetooth off the common + and the GND pad?

If so then I wouldn't have to mess with rectifying the track current I could use the decoder for all of what I needed.

Sumner

[peteski]

I have not actually installed them anywhere yet, but I did test one with my decoder tester.

The AUX "output" is a bit of a misnomer since it does not supply any voltage - it provides a switched connection to GND, with the the other lead of the device being controlled connected to U+ common positive. But the name has stuck because most model railroaders are not trained in electronics.   But I suppose that if you want to be able to turn your circuit on and off using a DCC function, you could connect it between AUX output and U+.  But there will be some voltage drop at the AUX "output" switching transistor.

As you mentioned, since this decoder has pads for U+ and GND, you can utilize it as your power supply.  But I would be leery of using that tiny decoder for powering all your modules (audio amp, 5V converter and the blue BlueTooth module) from it.  I don't  think that 1A rating is for continuous current draw.  Still, I suppose that since you got those decoders for ridiculously low price, even if you damage one there is no big loss.

[Sumner]

Thanks, looking at these decoder (our cheap ones) Looks like they can do anything that I'll need to do with my DC to DCC installs.  What is the difference between them and the newer ones?  Seem to be as small as the ones I have been buying for $30 and 4 functions is about all I ever need (newer ones have a couple logic ones).

I'll only be using the AUX functions for lighting.  The motor only draws 35ma and it will run on the motor outputs so that I can control its speed with the throttle.  I'll check the amp draw for the 750mw amp and the Bluetooth receiver but from specs they look to maybe total 70-80ma.  Like you said I don't have much to loose ($8) so will give it a try (breadboard first).  I'll report back.

Sumner

[peteski]

Those ESU decoders are perfectly good LokPilot decoders. Their firmware can even be updated if you have a LokProgrammer. They don't have as advanced BEMF tunability as the LokPilot V4 or 5 decoders, but they are still excellent decoders (better than many other brand decoders).

[$2 Bill]

I have 100 microfarad 16 volt. I have 47 microfarad at 25 volts. Could I use two of the 47 microfarad to replace the 100 microfarad cap?

You need them wired in Parallel for 94µF. (math is "Backwards" to Resistor use.)

I notice the 16v Cap on the Amp... I'm guessing "max" volts for that board is 15v to run on 12v but still may not last long for your application.

You may need to add some kind of 12v regulation for that board. 12.1v Zener with resistor might work. Resistor keeps the Zener from frying when sees > 12.1v. They make other regulators like 7805 7809 or 7812 etc but likely need "low cutoff" versions for 12v if DCC outputs is 13-16v.

Why?
"12v" on DCC may or may not be accurate sim to real cars most saying have "12v systems" must have 12v but nope because have higher volts when engine running, 13.5 to 14.7v, so the alternator will charge the battery. Other things can make volts higher or lower too. If you measured DCC volts with a meter, DCC make that "wrong" for sending data on the tracks. Or thinking DCC act like PWM but you never see 100% Duty Cycle for same reason. The meter is "wrong" because meter is try to read "RMS" volts even on DC ranges whether or not meter is labeled as "True RMS." (That label means the meter is "smarter" and doesn't care so much about shape or frequency.)

Is why many old things stopped working because was simply working @ top edge of volt range to start.

[peteski]

That large capacitor rated 16V on the LM386-based audio amp seems to be connected to the amp's pin 5. That capacitor is used as AC coupling for the speaker (not connected to the power supply rails. I doubt it will ever see the power supply voltages.
Here is an example of such circuit:



 But I do agree that if there is any AC ripple on the supply voltage, it might be heard through the speaker. Regulated voltage would be best. Actually the audio amp would work powered from the 5V power supply as LM386 can operate from 4V - 15V. But since Sumner is experimenting, he can build the circuit as-is and decide if it is optimal.