Sunday, February 17, 2019

How I installed an Acme Engineering multi-cylinder diesel sound card in my HGLW loco

Last year, I constructed an HGLW diesel loco from a kit (see How I constructed an HGLW loco kit and How I detailed my HGLW loco). Most of my locos have sound cards and I thought for a while how I would add sound to this loco. Ultimately, I decided to opt for an Acme multi-cylinder diesel card as I have not had any previous experience with them and wanted to see what they were like.

I sent off an email to Mike Ousby (Mr. Acme Engineering) as at the time he was experiencing problems with his website ( and, after parting with £40, the card and accoutrements arrived the following day.

My first idea was to keep things simple and install the card as a completely separate circuit, using the battery and holder as supplied. However, space was tight inside and under the loco and, although I could have just squeezed the and battery inside the back of the cab, there was no room for the speaker. I decided to use a smaller encapsulated speaker which I had purchased from Rapid Electronics some time ago (

This would just have fitted in the cab with the card and the battery, however I felt it looked very cluttered, so I decided that, if I doubled the number of li-ion cells in the loco from one to two, the resultant voltage (7.4v) would be sufficient to power the card as well as the loco. Without the need for the 9v battery, this would mean I could easily fit the card and the speaker inside the back of the cab.

The loco was dismantled .....

..... and the single cell removed from its cradle. Fortunately, I had a spare cell from the same pack that the original cell had come from and so they were matched.

NOTE: You should never mix and match li-ion cells. Even cells with the same Amp Hour values may have quite different characteristics. When making-up li-ion packs only use identical cells bought at the same time from the same supplier. I get all my cells from Ecolux who guarantees the quality of the cells he supplies and will attach solder tags for free. He will also make battery packs of any size and shape on request.

The two were wired together in series with a 2S li-ion battery protection board and re-mounted on the cradle.

My next decision was how to supply power to the card. The simplest way would have been to wire it up directly from the switch supplying power to the receiver and another lead to the negative supply to the receiver. This would mean that the sound would come on all the time the loco was turned on. It would also mean the sound would continue when the loco was stationary. My next thought was to wire in a new switch to enable the sound to be turned off independently of the receiver and motor. But then I remembered that the Deltang Rx65b has outputs which can be controlled by the transmitter. I would just need to use one of the three buffered outputs (A, B, C or Pads 13, 14 and 15) which are capable of switching up to 2 amps. Simples!

So, a two-pole plug was wired-up, the red lead connected to the output from the switch going to the Deltang Rx65b receiver, and the black lead connected to Pad 15 (C) of the receiver. This pad would give me a switchable 0v output in response to the bind button (Ch5) being pressed on the transmitter. However, the output from P15 is momentary by default, ie 0v is only supplied while the button is being pressed. I wanted to change the output to latching, so that it would toggle from off to on and vice versa when the bind button was pressed. This required the receiver to be re-programmed. This was done by binding the receiver to one of my Tx20 transmitters and putting the transmitter into programming mode. (see How to reprogram a Deltang receiver with a Tx20).

The coding used to reset Pad 15 to latching output was 3, 15, 2, 5, 3. (ie Menu 2, Pad 15, latching output, Channel 5 (bind button), start high and toggle when the bind button is pressed). This might sound like gobbledegook, but hopefully reading through this section on another blog post might make it clearer - How to look up programming codes for Deltang Receivers.

The leads from the two-pole socket were passed through from the bonnet to the cab, through a couple of small holes between the feet of the driver.

The power leads were then connected to the Acme Engineering soundcard.

The speaker was then also connected. The red jumper lead was left in place on the soundcard as I wanted the sound to repeat continuously.

 Fully wired-up, the circuitry looks like this.

As can be seen, the two li-ion batteries are connected to the protection board before the board passes power to the switch. The board protects the batteries from short circuits, over-charging and most importantly, over-discharging. If the charge in a li-ion cell falls below 3v, then it will become permanently damaged. The auto-reset fuse is not really necessary with the protection board, but was already wired-in on the original circuit and so I left it in place.

You'll notice also that the sound card is wired-up to Pad 15 (aka Pad C) to provide 0v (ie the negative supply) when the bind button is pressed on the transmitter. The positive supply for the sound card is provided by tapping into the lead from the switch to the receiver.

I use both the two-way switch and the built-in isolation switch in the DC socket to ensure that the receiver cannot be turned-on accidentally while the batteries are being charged. Either one or the other would be sufficient, but I have now got into the habit of using both.

Heavy duty sticky pads were stuck the the back of the card and the speaker ....

.... and the speaker and sound card stuck inside the back wall of the cab where they are reasonably unobtrusive. I might eventually cover them with some cream coloured card, but for now I hardly notice they are there.

The loco was then reassembled and taken outside for testing. The sound isn't loud, but that might be because I am using a smaller speaker than that provided. However, the digitised sound is realistic and varies slightly as the loco trundles along.

The pace of the sound doesn't vary in relation to the speed of the loco however, and there is no engine start-up and wind-down as is provided with the MTroniks soundcard. However, the MTroniks card is more expensive and is not supplied with a speaker, battery, switch (which I didn't actually use - but will go into stock) and wiring.

I do feel that adding sound to a loco out in the garden is quite important as it adds to the atmosphere. I tend to keep the sound turned down on all my locos as I don't want to disturb the neighbours or their dogs and also am not anxious to draw attention to the passers-by that there is a railway behind that fence. So I am not anxious to increase the volume of the sound in this installation. As long as I can hear it, that's all that is needed.

The Acme Engineering sound card is a relatively inexpensive way of adding sound to a loco. My installation is a lot more complicated than it needed to be. The simplest approach would have been to put the whole thing in a truck which is towed behind and this would have the added bonus that any loco towing it would be given a voice. However, I like my locos to be self-contained and enjoy the challenge of tailoring an installation to suit my needs.