Saturday, July 30, 2016

How I trigger effects on a MyLocoSound soundcard with a Deltang/RC Trains Rx65b receiver


The latest version of the large scale MyLocoSound Universal soundcard includes five sound effects in addition to the sound of the engine.
On the steam soundcard, these are:
  • a plain or US style chime whistle;
  • a bell or short whistle;
  • a guard's whistle or 'All aboard' cry;
  • a safety valve blow off;
  • a Westinghouse brake pump.
On the Universal diesel soundcard these effects are:
  • a British two tone horn or a US-style single tone horn;
  • a bell (or reverse two tone horn);
  • a guard's whistle or 'All aboard' cry;
  • a turbocharger;
  • an airbrake release.
These effects (in addition to adjusting the chuff rate) can be triggered on the fly using the TV style remote control which is provided with the card.

However, as the TV remote is infra-red, it can only be used at short distances out of direct sunlight. Fortunately it is possible to trigger the effects using a radio control receiver, provided it has 0v outputs (ie outputs which will effectively connect the soundcard trigger terminals to the negative supply from the battery). The RC Trains / Deltang Rx65b receiver / controller has up to fifteen outputs which can be configured to provide this sort of output. By default, the receiver has at least five outputs which are suitable for triggering soundcard effects (Rx65b version 611/11 onwards - shown by 11 / 11 on the main chip in gold), and so, when I took delivery of a MyLocoSound Universal steam card, I decided to interface it with the card.

Wiring up the Rx65b

Consulting the chart on the Deltang website and the RC Trains Rx65b leaflet, I discovered the following output pads were suitable for triggering the MLS Universal soundcard with a Deltang / RC Trains Tx20 transmitter.
  • Pad 3 - 0v output when Ch2 goes low
  • Pad 4 - 0v output when Ch4 goes low
  • Pad 9 - 0v output when Ch3 goes low
  • Pad 10 - 0v output when Ch3 goes high
  • Pad 15 (C) - 0v when Ch5 goes low
So, what does this mean? Let's assume, for convenience, that when it is first switched on, a transmitter is sending no signals on any channel to a receiver which is bound to it - in effect, the channels are in a 'neutral' state. Twiddling a knob, moving a joystick, flicking a switch or pressing a button on the transmitter can make a channel go high or low depending on which direction the knob is twiddled, the joystick is moved or the switch is flicked. So, on the Deltang/RCT Tx20, when:
  • Function button 1 is pressed, it makes Ch2 go low;
  • Function button 2 is pressed, it makes Ch4 go low;
  • the Direction switch is flicked to the left, it makes Ch3 go low;
  • the Direction switch is flicked to the right, it makes Ch3 go high;
  • when the Bind button is pressed, it makes Ch5 go low.

This means that the Deltang / RCT Tx20 is able to trigger certain output pads on the Deltang/RCT Rx65b receiver which in turn can be used to trigger the sound effects on the MLS soundcard - Simple!

Armed with this information, I soldered colour-referenced leads to each of the relevant output pads on the Rx65b;
  • blue to Pad 3
  • orange to Pad 4
  • grey to Pad 9
  • purple to Pad 10
  • brown to Pad 15 (aka Pad C)

Wiring up the MyLocoSound soundcard

The MyLocoSound Universal soundcard has screw terminals for its input triggers. To trigger each sound, the terminal needs to be connected to the negative supply (0v). This could be done by attaching a series of push-buttons or reed switches to each terminal. As the Rx65b receiver can supply 0v outputs from its output pads, I could have connected leads directly from the pads on the receiver to the inputs on the soundcard. However, I knew that the 'internal' voltage used by the soundcard is 5v, whereas the 'internal' voltage of the receiver is 3.1v and so I recognised that there could be a possible conflict if residual current was to flow back from the card to the receiver. To help guard against this, I decided to connect 1k ohm resistors between the soundcard trigger terminals and each of the pads on the receiver. There's a possibility I could be being overly cautious, but having 'fried' a couple of receivers in the past, I felt the minimal cost of a handful of resistors was worth it.

That's all I needed to do - apart from connecting the speaker, the motor leads and the power supply to the card and receiver. If you are using a different battery supply for the soundcard to that used by the receiver, you would need to connect the negative terminals of each battery supply together (but NOT the positive terminals), to ensure continuity of the logic circuitry.

All that was needed now was to play with test the loco:

The output pads of the Rx65b are programmable and so any of the pads on the receiver could be used to provide 0v outputs. If, for example, you find that you have an earlier version of the Rx65b (ie the gold numbers on the main chip on the board aren't 11 / 11), then you could reprogram them (see How to reprogram the output pads on a Deltang / RC Trains receiver). Alternatively, if your transmitter doesn't have five accessory outputs, then some of the effects on the soundcard could be triggered by connecting reed switches between the inputs and 0v and using magnets placed between the rails.

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