Home Brew DCC control of Dapol Servo operated signals

[melmerby]

Following Jenny Kirk's review of the Dapol servo operated bracket review I decided to buy some.

I ordered them before Christmas and now have 3 in my possesion.

 

As supplied they are manually controlled from a changeover switch, one per arm, however I wanted to control them from DCC.

Dapol supply a TrainTech sourced unit (Dapol 4A-001-002 / Train Tech SC4) to convert to DCC but it is IMHO expensive as 1 unit controls just two arms and costs around £40.

An alternative is the Digikeijs DR4018 which is more economical.

 

I decided I could devise something much simpler to work off an Arduino configured as a DCC accesory decoder.

 

The voltage used for the operation of the arms is 5v off load but drops to around 2.5v if using a permanent changeover switch as supplied, the current is less than 0.03mA through the contact.

My first thought was to use 5v operated changeover relays driven from the Arduino and I ordered some suitable ones.

However thinking further I thought it should be easier than that.

I had a couple of LTV817 optocouplers (Basic DC input devices), I tried them and they work perfectly

Driven at about 20mA forward current input, they switch on enough to operate the signals perfectly.

 

I have ordered some LTV847, these are the quad version of the same device and will require one per dual arm signal. The ones I have ordered (UK supplier) work out at £2.10 each including postage for 5.

More to follow as I progress

Edited December 28, 2021 by melmerby

[melmerby]

Quick video of proof of concept, which show the minimal component count to make it work.

 

 

Watch on You Tube

 

EDIT

Strange, couldn't get the video  to work on the PC it was posted on.

However it'll work on another computer!

Edited December 30, 2021 by melmerby

[melmerby]

I have now made two boards up using this concept, the first using an Arduino Uno clone (difficult) and a Nano Clone (easy)

 

These are the results.

Uno (not so easy):

 

The board is 14x8cm

I intended using a proto shield but could not fit the components on to it, so hade to reverse the idea and convert the UNO to a plug in using pin headers as used on the Nano

This met with the problem that the designers decided to make the break between D7 & D8 0.15" which upset the pin spacing (the break between Vin & A0 is 0.2" so keeps to the 0.1" pin array.

I got around this problem by dog-legging D8 onwards by 0.05" so they would line up with a socket on the stripboard.

 

Nano (easy):

 

The board is 8x8cm and all the pins on the Nano are 0.1" spacing, so line up with the socket.

This was a doddle.

You can see the full component count on this version.

 

Edited April 7, 2022 by melmerby

[two tone green]

Sorry to divert from what you are proposing but you mentioned the Digikeijs DR4018, how would this work? 

[WIMorrison]

I have used a DR4018 to switch Dapol signals on a friends' layout. I simply used the DR4018 to switch a 12v relay in place of the Dapol switch for each signal.

 

Works a dream, but what might have been better would have been to use latching relays rather than having the DR4018 holding the relays on.

[two tone green]

Ok so using the 4018 as a switch and it’s -ve output from its terminals to operate the relay. 
 

I have some nice little TTL relays left over from my DC days and TTL based automation which may fit the bill. 

[melmerby]

2 hours ago, two tone green said:

Sorry to divert from what you are proposing but you mentioned the Digikeijs DR4018, how would this work? 

Hi TTG.

It was in Dapol's instructions where they suggested, if not using the dedicated unit, to use a DR4018 as it can be used as a zero volt switch. They emphasise that you should not use a switch decoder that outputs any voltage as it could damage the signal unit.

(I have a DR4018 but I cannot see that option in the instructions.)

That's why I decided to make my own and settled on optocouplers which do provide a suitable switch.

The switching circuit on the Dapol unit is fairly high impedance so an imperfect switch such as an opto output is works a treat.

In my case the opto outputs are about 75ohms in the "on" position, which is more than adequate for reliable operation.

The input is driven at about 10mA.

 

[two tone green]

1 minute ago, melmerby said:

Hi TTG.

It was in Dapol's instructions where they suggested, if not using the dedicated unit, to use a DR4018 as it can be used as a zero volt switch. They emphasise that you should not use a switch decoder that outputs any voltage as it could damage the signal unit.

(I have a DR4018 but I cannot see that option in the instructions.)

That's why I decided to make my own and settled on optocouplers which do provide a suitable switch.

The switching circuit on the Dapol unit is fairly high impedance so an imperfect switch such as an opto output is works a treat.

In my case the opto outputs are about 75ohms in the "on" position, which is more than adequate for reliable operation.

The input is driven at about 10mA.

 

Hi.  
I have four 4018’s on the layout and use them to switch lights on and off in buildings etc and to operate my servo driven level crossing with the 16 outputs configured as switched -ve, common ground outputs. Also allows dimming by adjust CV’s. 
 

So good news then, I can use the 4018’s for the signals without any extra components. 
 

Thanks
 

 

[two tone green]

Read page 31DR4018-Manual.pdf

[two tone green]

So for about £35 you can control 16 signals. 
A bit cheaper than Dapols offering. 
 

Plus other outputs not being used for signals can control other items 

[melmerby]

1 hour ago, two tone green said:

Read page 31DR4018-Manual.pdf

 

53 minutes ago, two tone green said:

So for about £35 you can control 16 signals. 
A bit cheaper than Dapols offering. 
 

Plus other outputs not being used for signals can control other items 

Thanks. I assume you mean preset 1?*

I'm looking at my DR4018 right now.

 

In that case I would think you need two outputs (one complete changeover) per signal as that is what the signal needs. The contacts can be momentary as after switching, the contact can be removed and the signal will only change position when the other contact is operated.

Therefore only 8 signal arms for £35.

 

Mine does 4 arms for about £10-12 plus 3 spare switched outputs (not shown) for other uses.

 

EDIT

* I discounted preset 1 as on p28 it shows it powering two LEDS!

Edited January 28, 2022 by melmerby

[two tone green]

Yes, preset 1. 
 

I thought the switch had two wires on so acting as an off on switch so one output of the 4018 per signal would be enough. 
 

I don’t have a signal so can’t test anything. 

[melmerby]

Just now, two tone green said:

Yes, preset 1. 
 

I thought the switch had two wires on so acting as an off on switch so one output of the 4018 per signal would be enough. 
 

I don’t have a signal so can’t test anything. 

It's a changeover switch so you need a common and two other contacts, they dont have to be permanently made so you can use a normal changeover, a passing contact changeover, a latching  pushbutton changeover or two separate momentary push buttons ( all are shown in the instructions.)

[two tone green]

Thanks. 
 

I am awaiting the O gauge bracket signals so may have a bit of a wait before I can play. 
 

But with the 4018’s and RR&Co I am sure I can get some kind of operation out of them. 

[melmerby]

1 minute ago, two tone green said:

Thanks. 
 

I am awaiting the O gauge bracket signals so may have a bit of a wait before I can play. 
 

But with the 4018’s and RR&Co I am sure I can get some kind of operation out of them. 

I've three of the GWR brackets, so are well into playing with them.

 

Looking at the Arduino again, I realise I could use the analogue pins as switched outputs as well, that would allow another 4 signal outputs, thus equalling the DR4018's 8 signal outputs.

Just need two more LTV847 and 8 x 330R plus some sockets, should come in around £20 total for 8 signal outputs.

 

 

[two tone green]

I assume it’s the 4mm ones you have. 
 

I was speaking with the guys at Tower models and they don’t know when the 7mm version will be in. 

[melmerby]

Yes 4mm ones.

IMHO they are a good attempt at a ready to plant working signal, a little crude in places but probably the best yet.

The O gauge ones seem to have a finer level of detail all round, complete with balance weights.