Deltang advice

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BorisSpencer
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Deltang advice

Post by BorisSpencer » Fri Jan 11, 2019 11:55 am

I am thinking of biting the bullet and dipping my toe into the scary world of RC.
This I have decided will entail an investment in a TX22 and 2 or 3 x RX65C-22 receivers, more will follow if these prove successful.
So a couple of questions for a resident Deltang experts.

These will only be for my battery powered locos most of which run on 2xAA or 2xAAA batteries which at 2.8v is not enough to power the receivers.
The next problem is the two-color LEDs that I have installed, these show yellow or red dependent on polarity and change on a DPDT along with the motor power. I have found this a really easy way of cramming directional lighting into a small space.

I believe I can get around the power requirement by using 1x18650 or 1x10440 lithium ion cell along with a dummy cell (a dowel with a copper core) in the existing battery boxes, this should provide a nominal 3.7v, and leaves me an easy option to change back to manual control.

Questions:
1. is my battery assumption valid?
2. having read the spec sheets, can I wire the LEDs to a combination of Pads A, B, 1, and 2? i.e. Each LED would have one leg attached to both Pad A and Pad 2 with the other leg attached to both Pad B and Pad 1, athough I suspect I would also need to add an appropriately facing diode on each connection.

I apologise for the rather long winded post, but I don't want to spend £150-£200, without understanding the limitations.
If this works I can see some exciting times ahead playing with the advanced functions like station stop etc.

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Re: Deltang advice

Post by BorisSpencer » Fri Jan 11, 2019 1:01 pm

In response to my own question I wonder if it will be easier to change over to three-legged bi-colour LEDs.

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Re: Deltang advice

Post by tom_tom_go » Fri Jan 11, 2019 1:20 pm

The Rx65c support directional lighting, will this not cover what you need?

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Re: Deltang advice

Post by BorisSpencer » Fri Jan 11, 2019 2:20 pm

Hi Tom,
The problem is that I have used 2-legged bi-colour LEDs, when you put a current across them one way they light up yellow, and when you reverse the polarity they light red. This means with simple on-off locos I have wired them to the motor terminals, but with the Deltang they provide 4 terminals - switched 0v and switched 3v for each of Front and Back, I just need to know if I can combine them.

The suggested use is to have either the Cathode or Anode wired to the battery and the other side switched.

As an example I have an IP-Engineering Lollipop Tram, which has two lamps on the front which light yellow or red directionally, this is done with only two wires instead of having to have both yellow and red LEDs. And to add to the problem they're all glued in!

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Re: Deltang advice

Post by tom_tom_go » Fri Jan 11, 2019 3:11 pm


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Re: Deltang advice

Post by ge_rik » Fri Jan 11, 2019 4:35 pm

Hi Boris
To address the questions you pose

1. Almost. The 18650 is larger than an AA battery so you need to use a 14500 - 10440 is AAA equivalent
2. Tom's pointed you to the page on my blog which answers this (hopefully) - though I see in a later post you are using 2-leg bi-colour LEDs which will not be as easy to interface with the Rx output pads.I'll do a bit of head scratching and see if I can sort something out for you given the LEDs are glued in.

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Re: Deltang advice

Post by BorisSpencer » Fri Jan 11, 2019 5:22 pm

Cheers Rik,
I thought I'd read all your pages! I must have missed or forgotten that one, and also some of the informative links that lead from it.
I originally considered using 3-legged LEDs, but never had any intention of using remote control, obviously in hindsight a poor decision.
The one saving grace is that I have loads of room in the back of the Lollipop to cram in any convoluted wiring and circuitry. My rational at the time was connecting to the front lights as unobtrusively and easily as possible.

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Re: Deltang advice

Post by ge_rik » Sat Jan 12, 2019 9:10 am

Hi Boris
I've scatched my head (and those of Greg and Phil) and we have three possible solutions.

1. The most promising is to control the directon lighting with a 3v dpdt relay. It would have to be triggered by a couple of pads, maybe those connected to the direction switch (ch3). The disadvantage is that it wouldn't be automatic.

2. You could connect the LEDs across the motor outputs but might need a capacitor (eg 1uF) across the terminals to smooth the supply. Disadvantage would be that the lights will extinguish when slowing and stationary.

3. You could try connecting the LEDs across the two sets of directional outputs. Eg P1 provides 3.2v and Pad A provides 0v when going forward. So if you connect the legs to those pads it MIGHT work. Similarly, if you then connect the legs the opposite way round to pads 2 and B it should switch the polarity. HOWEVER - this is theoretical rather than tried and tested. I don't have a spare rx to try it and there is a risk you might blow the rx circuitry. I've no idea how the wiring on the boards and inside the logic chips is arranged (no one but David T (Mr Deltang) does). Given the outputs from A and B are buffered by FETs then you might get away with it. However, I would connect resistors to both legs and increase their value to limit the current to 5mA (say 2 x100R) to be on the safe side. I hasten to add that this is only a theoretical solution - untried and untested and I cannot guarantee that it will not blow the circuitry on the rx. If I was still running RC Trains I would give it a try, but now I have to pay full price for my deltang stuff I'm not anxious to give it a try. I'll try sending an email to David T, but now I'm no longer one of his agents I'm not sure he would respond. I'll give it a try though and let you know the outcome.

Rik
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Re: Deltang advice

Post by tom_tom_go » Sat Jan 12, 2019 9:17 am

Changing the LED's would be the easiest option?!

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Re: Deltang advice

Post by ge_rik » Sat Jan 12, 2019 9:45 am

ge_rik wrote:
Sat Jan 12, 2019 9:10 am
1. The most promising is to control the direction lighting with a 3v dpdt relay. It would have to be triggered by a couple of pads, maybe those connected to the direction switch (ch3). The disadvantage is that it wouldn't be automatic.
Actually, on reflection, you could trigger the relay from the A and B outputs from the Rx and then get auto directional lighting. As these outputs are buffered they should be able to handle the load of the relay.

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Re: Deltang advice

Post by philipy » Sat Jan 12, 2019 10:10 am

tom_tom_go wrote:
Sat Jan 12, 2019 9:17 am
Changing the LED's would be the easiest option?!
I'd have thought so myself. Simply, carefully drill the old ones out and glue new ones in. They are so cheap it isn't worth the struggle to go the complicated electronics routes.

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Re: Deltang advice

Post by ge_rik » Sat Jan 12, 2019 12:41 pm

I got a reply from David T, and he advises against it (ie option 3). He doesn't say it won't work but is concerned about shorting the P outputs to ground, in effect saying he's not sure what will happen - ie it's an untested scenario.

So, my advice would be to either go down the relay route or, as others have suggested, replace the 2-leg LEDs with 3-leg.

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Re: Deltang advice

Post by ge_rik » Sat Jan 12, 2019 1:01 pm

Further to the above, if you used a 3v version of this - https://www.ebay.co.uk/itm/111371029236 - you need only wire the coil up to the B pad on the rx65 (and also to the battery, maybe through a voltage regulator, not sure if it will handle the 4+v the li-ion can reach when fully charged). This will switch the contacts when in reverse and when going forward the relay will revert to its default. You won't need a latching type as the output from B will be constant while in reverse.

Hope that makes sense. I'll sketch out a circuit diagram if you need one.

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Re: Deltang advice

Post by metalmuncher » Sat Jan 12, 2019 10:49 pm

I think Rik's 'option 3' should work if you put the LEDs across P1 and P2 instead of the buffered drives.
From the looks of it pads P1 and P2 are directly connected to the IO pins of the microcontroller:
Image
The datasheet for the MCU says IO pins should be able to sink or source 25mA absolute maximum, 15mA normally, and the total current for PORTD shouldn't exceed 100mA. As long as you use suitable resistors to lower the current, say 5mA total (remember you will have a front & back LED lit at the same time) you should be OK.

This is not an uncommon configuration, Microchip even has an application note on using this method for more complicated LED arrays: http://ww1.microchip.com/downloads/en/A ... 91029a.pdf while this isnt the same brand MCU as in the deltang board, the IO pins work in a similar way.

Disclaimer: While I have done this on similar Atmel microcontrollers, I haven't tested this on a deltang board. I am not an electrical engineer, just a hobbyist. ;)

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Re: Deltang advice

Post by BorisSpencer » Sun Jan 13, 2019 11:35 am

Thank you all for your help, I think I will go with Rik's suggestion of a DPDT relay (now ordered), I hadn't considered this and it will actually then replace the existing direction switch so will keep the rewiring to a minimum.

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