5v or 6v start ideas ?

[Dtsteam]

Another plea for help....
I want to play with some form of on-board resistance, so that the loco motor doesn't turn until there's 5 or 6v on the track.
My usual ham-fisted way would be to make 2 strings of 10 diodes in opposite directions, but apart from the fact that its a lot of diodes, I can't help thinking there must be a better way .... Any suggestions please ?

 

[dutchelm]

Re:5v or 6v start ideas ?

Diodes will work better than resistors as they have a constant voltage drop whereas the voltage drop with a resistor is load dependent. However 10 seems rather a lot. Try about 6 each way to start & then add more until the desired result.
I needed to do this to one loco so the sound started before the loco moved off.

 

[Tony Walsham]

Re:5v or 6v start ideas ?

A good sound system can usually read the first 1 volt on the track and start up using the sound system back up battery.

 

[muns]

Re:5v or 6v start ideas ?

Massoth make a DC motor control unit that holds back the motor so that there needs to be about 6v track power before the loco moves off so that sound cards/lights etc can be operative when stopped.

power to the motor is then controlled in such a way that at full power (22v) all is passed to the motor so you don't loose the top speed.

http://www.gardenrailoutlet.co.uk/massoth-dc-motor-control

(corrected the link)

 

[Neil Robinson]

Re:5v or 6v start ideas ?

My usual ham-fisted way would be to make 2 strings of 10 diodes in opposite directions, but apart from the fact that its a lot of diodes, I can't help thinking there must be a better way .... Any suggestions please ?

Should you wish to continue with the diode string method you only? need the number of diodes for one direction plus two. In other words in the case quoted above a total of 12 rather than 20. I hope these diagrams make it clear, the diodes conducting are shown filled in black.

 

[Madman]

Re:5v or 6v start ideas ?

Threads like this are my Electronics education. I have no clue if I will ever get a diploma in "Hamstring Electronics" however.

 

[Dtsteam]

Re:5v or 6v start ideas ?

Me neither, Dan, but in my book if you don't ask you don't learn.
Neil, thanks for the suggestion, I thought there must be a better way than two arrays back to back, but I couldn't see it.