Connecting DP8 to activate flashing LED

[geoffwbasig]

I thought I would try connecting a spare output on my DP8 to a flashing LED which was previously powered by a simple on-off button in a 12v dc circuit.  The spare output has an address of 37 (the DP8 was configured with 30-37 when I initially set up) but when I operate that accessory number the LED does not come on. I have tested the LED on a 9v PP3 battery and it works from that.  I am just wondering whether I have missed a programming step?

[Paul Harman]

Hi Geoff

The DP8 only gives out a short pulse which is unlikely to be visible. It is possible to add a 'D' type latch (such as a CMOS 4013) between the SC1 and DP8 to latch the pulses.



4013 is available from Maplin as part QX07H

[geoffwbasig]

Thanks Paul, this flip flop device would appear to be the answer although it seems to be designed to fit on a circuit board. I think I might have a spare bit of circuit board which I could utilise. I notice that there are seven connectors each side plus one at each end, so I would be grateful if you could explain exactly how it is wired up. I have heard of flip flop devices but know absolutely nothing about them!

[Paul Harman]

Hi Geoff

You will need a small piece of stripboard with at least 7 strips, and a 14-pin IC socket (Maplin BL18U)

You can wire to the IC socket, and then plug the 4013 in when you have done. Here is a picture showing the pin numbering when viewed from the top (pins pointing away from you). Just remember to cut the tracks under the IC on the stripboard before soldering it all up.




There will be a notch in the socket at the pin 1 end, and probably in the 4013 too.

[geoffwbasig]

Hi Paul

I've wired everything up exactly as per your diagram and using the Maplin 4013 but can't get the LED to work. Strangely, last night when I first switched on ,the LED did flash permanently but I couldn't turn it off except by powering down.This morning the LED won't light at all.
When I originally set up the DP8 I set CV38 to 15 and then set up the CV addresses to start at 30 , so I have 30-37 addresses set up. 30-33 are connected to 4 Dapols and these work OK. 34-36 are currently unused and I have wired up the LED to 37, but it doesn't work when I select that address on the controller.
I have double checked all my wiring and for shorts etc and I have checked the LED by running a multimeter across it so I know it is working.
Do I have to alter any CVs at all or maybe just re-program from scratch? Since the LED is connected to the DP8 I would have thought that CV38 would have to be left at 15?

[Paul Harman]

I don't think you can use addresses 30-37, you have to use two consecutive blocks of four addresses, such as 29-36, or 33-40. You will probably find that what you think is 37 is actually 29.

[geoffwbasig]

I'm afraid you've lost me a bit here Paul! I have four dapol signals connected to S1, S2, S3 and S4 on the DP8. I am using S8 for the LED. I have disconnected the original wires which connected 1 and 2 on the DP8 to H and K on the SC1 and used the substitute connections as per your diagram for the LED. Is this wiring correct and should I now be using a different setting for CV38?

[Paul Harman]

If you are using Dapol signals you cannot change the setting of CV38.

'A' - 'G' and 'k' on the DP8 should be connected to the corresponding terminals on the SC1

the 'H' terminals should be connected to the 4013 as per the diagram above if you want to operate the flashing LED.

There is nothing difficult about choosing a new address range, you need to decide which address range you want to use - 29-36 or 33-40. Your original choice of 30-37 is not valid, you cannot include addresses from three decoder address blocks (30-32 is one block, 33-36 another block, and 37 is in the third block).

[geoffwbasig]

Thanks Paul. I am now using the address range of 29-36 and everything works OK. I am afraid I did not read the original instructions properly, forgetting that the ranges were only valid in specific blocks.
Although I have been using DCC for a few years, I am finding that there is always something new to learn!

[Paul Harman]

Excellent that all is now well. Thank you for the feedback.