Hi all, I brought the MK134 from maplins, I was wandering if theres away of controling the sound in the actual layout, I:E, when a train starts of its sets the MK134 going and as I speed up so does the sound. Can any body help

 

Hi all, I brought the MK134 from maplins, I was wandering if theres away of controling the sound in the actual layout, I:E, when a train starts of its sets the MK134 going and as I speed up so does the sound. Can any body help

It might have been easier for us if you had mentioned that this was a Velleman Minikit MK134 "STEAM ENGINE SOUND GENERATOR WITH WHISTLE" :http://www.velleman.eu/products/view/?id=347727

Here is a link to the manual for this kit:http://www.velleman.eu/downloads/0/minikits/manuals/manual_mk134.pdf

Unfortunately the "speed" control (RV1, 100kΩ: see diagram in manual) is a resistance inside an oscillator circuit, it does not simply act as a voltage source. 7

In principle, there are things that might be done to change this, but if you made a mistake the kit might not work any more.

How much experience have you had with electronics?

 

Hi Adjuster, I have built a few projects, not hot on electronics, I tend to follow cicuits and build what i need. I brought this for the father inlaw. He has quite a big layout, would be nice if i can get this going for him...

 

Sorry forgot to mention what the MK134 was, I had found this idea on you tube,( LGB home made steam sound). This is what gave me the idea for the layout at the father inlaws.

 

OK, so you are at least an adult, and not a youngster playing with his Christmas present. It will be less of a tragedy then if something goes wrong.

The trick would be to provide a voltage-controlled oscillator, with a rate depending on the input. In principle, this could then be controlled by the track voltage.

The starting point would be to analyse the present circuit around IC1D, and then cook up an alternative, either around IC1D or perhaps on an added circuit.

Have you ever used a circuit simulation program?

 

Hi, I've never used one before, only design software free of the web, I know Maplins do one that i can get for around £34. normaly i'm quite good at working things out. I don't mind frying the circuit, the lm324 are easy to come by. I've tried looking on the web for simlar circuits but keep coming up a blank. would you know of any links i could try.....Thanks

 

OK, here is a starting point - a simplified version of the oscillator in LTSpice. There is no LM324 in my version, so this uses another op-amp, despite what I've called it. It won't be exact, but I don't suppose it matters much. What's important is that we have a square wave oscillation at a few Hz, as expected.

My first thought is that you could make a separate circuit to be connected to the junction of RV1 and R19 to limit the voltage swing there. This is a fairly safe connection to make, and disconnecting it would put the circuit back as it now is.

The aim would be to have something like another LM324 to give a couple of DC voltages to feed a pair of clamp diodes. The voltages would have to centre on half supply with no input from the track, with a bit of offset so that the "steam" is at minimum until the "engine" starts. As the voltage comes up, one diode drive goes positive, the other goes negative, and with any luck we get an accelerating train sound.

 

Thanks Adjuster for your help, it is much appreciated. I had a look at you diagram, but as for the attached file on the lm324 i could not get to look at it, not to worry i still have the original diagram.....Once a gain thank you

 

Having thought about this a bit more, I'm sorry to have to say that I may have led you down a wrong path with the voltage clamp idea: it probably won't be good enough. The problem is that the oscillator cannot be slowed very much before it stops - a minimum voltage swing of about one third of the supply is needed.

It may be easier to replace this part of the circuit with a voltage-controlled oscillator.

 

If you need a voltage controlled resistor a photo resistor and an led might be used. Not sure if you have enough know how to work out the details ( even assuming a voltage controlled resistor is what you need )

 

If you need a voltage controlled resistor a photo resistor and an led might be used. Not sure if you have enough know how to work out the details ( even assuming a voltage controlled resistor is what you need )

That sounds like a brilliantly simple idea, and certainly worth trying. The OP is trying to get a train "chuffing" circuit to speed up as a model train is accelerating. The oscillator speeds up as a variable resistor is turned down.

A suitable LDR could be put in place of the variable resistor, and lit by a lamp fed by the track voltage. As the track voltage increases, the oscillator should get faster as required. Whether or not the result would be realistic is another matter, but it certainly has the merit of simplicity.

 

I would like to thank every one for helping me out with this, the LDR opption sounds brill. I have seen another circuit that uses the same principle. Being as they only cost a few pounds to buy so i will try both and see what happens....Once again i would like to say thank you...

 

You would also have to make sure that the oscillator would stop with minimum "steam" when the LDR was dark.

Possibly a large value resistance (a few hundred kΩ,exact value TBD) to ground from the 10μF capacitor would do this.