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RC Circuit Switch Question


BG John
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I'm building an Arduino based radio control receiver into a wagon, that I can plug unconverted DC locos into. It's powered by 4 x AAA batteries, providing around 4.8 volts. I've also got a step up converter producing 9 volts, and want to be able to switch between the two, so I can run 12 volt locos at a reasonable speed, as well as 3-6 volt locos. I'm not sure how to wire it.

 

This is a simple diagram of the possible positive wiring, with a SPDT switch between the battery and the step up converter, so I can bypass it. I'll also add an on-off switch to the battery for the whole system. This arrangement makes the output of the converter live when the motor driver is connected directly to the battery, which doesn't seem like a good idea. Can I just put a diode between the + Out on the converter and the motor driver, or do I need to do something more complicated? If so, is a 1N4001 OK, as they're the only ones I've got?

 

post-7091-0-35226100-1506004397.png

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Hi John,

 

The basic idea looks good.

 

I think adding a diode would be a good idea, although whether its essential or not depends on the circuit of the step-up convertor. You would lose half a volt or so across the diode. The 1N4001 should be OK, it is good for an amp and I don't suppose your motor will take that much current.

 

However, a better solution would be to use a double pole switch instead of a single pole one, and use one pole to switch the battery as you have it and the other to switch the motor driver input. Often a double pole switch is not mich bigger than the equivalent single pole one as its usually the mechanism that determines the size, not the contacts.

 

Frank

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Thanks Frank. I'd thought of a double pole switch too, but I've only got tiny single pole ones, and I'm trying to squeeze all this, and more, into a OO gauge van! I've got miniature double poles, but they're massive for what little space I've got available. At least I know both these options are viable.

 

These are the step up boards I've got. They only arrived this morning, so I haven't tried them yet.

https://www.aliexpress.com/item/1A-high-efficiency-DC-DC-Boost-Step-up-Converter-2-9V-to-9V-Power-Supply-Module/32741222813.html

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You could check whether the two GND connections on the step up board are common - they may not be. It is also possible that the two V+ pins are common. Check both.

 

The answer will affect how you wire the switch.

 

For example if the two V+ tags and the two GND tags are separate you will need a DPDT switch.

 

...R

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Thanks Frank. I'd thought of a double pole switch too, but I've only got tiny single pole ones, and I'm trying to squeeze all this, and more, into a OO gauge van! I've got miniature double poles, but they're massive for what little space I've got available. At least I know both these options are viable.

 

These are the step up boards I've got. They only arrived this morning, so I haven't tried them yet.

https://www.aliexpress.com/item/1A-high-efficiency-DC-DC-Boost-Step-up-Converter-2-9V-to-9V-Power-Supply-Module/32741222813.html

 

 

Surprisingly, Amazon UK have some tiny DPDT latching switches, they are 7x7mm, and about 12mm total height including pins, but it's possible to cut the long push button down by about 3mm, as well as the pins, so you might have room.  £1.93 for 55, post free. (They don't have any mounting arrangement, intended for pcb mount). They have lots of options if you search for "micro PB switch".

 

https://www.amazon.co.uk/Push-Button-Switch-Self-locking-Switches/dp/B01G6P1G8W/ref=sr_1_3?ie=UTF8&qid=1506027268&sr=8-3&keywords=micro+push+button+latching+switch

 

Mike

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Surprisingly, Amazon UK have some tiny DPDT latching switches, they are 7x7mm, and about 12mm total height including pins, but it's possible to cut the long push button down by about 3mm, as well as the pins, so you might have room.  £1.93 for 55, post free. (They don't have any mounting arrangement, intended for pcb mount). They have lots of options if you search for "micro PB switch".

 

https://www.amazon.co.uk/Push-Button-Switch-Self-locking-Switches/dp/B01G6P1G8W/ref=sr_1_3?ie=UTF8&qid=1506027268&sr=8-3&keywords=micro+push+button+latching+switch

 

Mike

That's incredible. I've just ordered two 8x8mm ones from the cheapest UK eBay seller I could find for £1.28! I was thinking they could be useful for loco switches, where maybe I could attach them to something like a tank filler, that sticks up when it's off, and is in the right position when it's on. Not sure what to do with all the 57 I now have on order though! Maybe I could put them on eBay :).

 

PCB mounting is fine, as most of what I'm doing needs a PCB somewhere, and I can always cut a small bit to use as a mounting bracket.

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  • 3 weeks later...

Surprisingly, Amazon UK have some tiny DPDT latching switches, they are 7x7mm, and about 12mm total height including pins, but it's possible to cut the long push button down by about 3mm, as well as the pins, so you might have room.  £1.93 for 55, post free. (They don't have any mounting arrangement, intended for pcb mount). They have lots of options if you search for "micro PB switch".

 

https://www.amazon.co.uk/Push-Button-Switch-Self-locking-Switches/dp/B01G6P1G8W/ref=sr_1_3?ie=UTF8&qid=1506027268&sr=8-3&keywords=micro+push+button+latching+switch

 

Mike

These switches arrived today, and they look OK. Only 53 in the packet though. Neither these, or the 8mm ones, fit on a PCB without bending the pins, that I haven't tried yet. They both have the right spacing one way, but not the other.

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Having bought one of the 9 volt PP3 sized lithium batteries with built in USB charger that Spotic showed in another topic, I think I'm going to use that for this job now. It should give enough to run 12 volt locos, and I won't bother with a lower voltage for low voltage motors. It will keep the job simpler.

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Having bought one of the 9 volt PP3 sized lithium batteries with built in USB charger that Spotic showed in another topic, I think I'm going to use that for this job now. It should give enough to run 12 volt locos, and I won't bother with a lower voltage for low voltage motors. It will keep the job simpler.

Hi John,

 

I've also drawn a blank when sourcing very tiny switches for BPRC, and I've got round this when using a PP3, by making up a battery holder where the battery can be easily removed, becoming, in effect the switch.  This also obviates the need for the normal clasp type terminals for these batteries, which are needlessly large.

 

post-28779-0-81086700-1507483488.jpg

 

I folded up a simple cradle from 22G sheet steel and fitted a bit of paxolin with two terminals turned up from brass rod, behind which is a 3mm pad of closed cell foam, which acts as an insulator and also provides the slight pressure on the battery, needed to ensure good electrical contact.

 

post-28779-0-73817800-1507483501.jpg

The wires are led out to one side, which has a Pololu voltage controller mounted in a piece of shellaced foamboard, and thence to the locomotive mounted Deltang Rx63.

 

In the little guards van I chose as the battery vehicle, there was no room for any switch that I could find, and even then I had to fit false doors and end panel to block the verandah at one end, but I think in a 10ft wheelbase van there would be room for a small switch.

 

post-28779-0-13188000-1507483524.jpg

 

 

I realise that this solution is not to everyone's taste, but it works well in practice, and I want to move on to building a small diorama entirely operated by radio - points, signals, dimmable street and building lighting and so on, as well as the locomotives, - so further refinements of the loco systems will have to wait a while !

 

Mike

 

 

Edited by Spotlc
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That's neat. I've just restarted my battery/RX van, except that rather than the Dapol van I was using, I'm putting it in an old Airfix GWR brake van. The advantage is that it has a removable roof, so I can attach the electronics to the body rather than making separate mountings. The plan at the moment is to fit one of these inside the veranda. It should glue to the side without being too obvious, and I can get my finger in to operate it (I hope!).

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