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Tx20S User Information

Tx20S is a hand-held wireless transmitter intended to control one model railway live steam locomotive. It has a large knob for throttle control plus a smaller knob for direction control and one push button which can be used to control a whistle servo.


  • Tx20S uses the 2.4GHz band which requires no frequency channel control and is very resilient against interference. All radio frequency components are contained on the internal Tx2 module. There are no user adjustable parts on this module and it should not be modified.
  • Tx20S is compatible with all DSM2 receivers; this includes all Deltang receivers and many Spektrum plus 3rd part Spektrum compatible receivers.
  • Any number of receivers can be bound to your Tx20S but only one should normally be switched on at a time to operate them independently.
  • Range is suitable for indoors and small outdoor sites; the outdoor free-air range to a Deltang receiver is at least 50m. Range indoors is affected by building construction materials, furniture, people and receiver installation.
  • The throttle and direction knob movemements and bind push button action are transmitted as separate R/C 'channels' which must match the receiver configuration:
throttle:channel 1
direction:channel 3
bind button:channel 5


The Tx20S uses a PP3 9V battery, preferably Alkaline or NiMH / Lithium rechargeable. The maximum working voltage of the internal electronics module is 10V and there is a protection diode wired in series with the battery lead. This allows the battery voltage to be up to 10.7V. If the battery voltage is above this value, the internal regulator will shut down and the transmitter will not operate.

To replace the battery:
  • Make sure that the power on/off button is off (up) before) adding or removing a battery.
  • Remove the lid at the bottom rear of the case by sliding it downwards. When Tx20S is new this will require a bit of effort to slide it past the retaning 'click'. The image at the right shows the case rear with the battery lid removed.
  • Remove the battery from the compartment and pull the battery clip off the terminals. Replace the clip on the new battery which will only fit one way round. TAKE CARE, if force is needed, the connector is probably the wrong way round.
  • Replace the battery cover by sliding it up from the bottom making sure that the retaining tab goes under the case rear. The battery is held in place with a piece of foam attached to the cover and you will feel some resistance as the cover is pushed down onto the battery.

On / Off Push Button

The Tx20S has an illuminated push-button latching on/off switch. The LED lights continuously when the transmitter is on and flashes when Tx20S is in bind mode (see below). It is best to switch the transmitter on before the receiver. If a receiver is switched on with Tx20S off, it is likely to enter bind mode with rapid flashing of the LED on the receiver board. If you did not intend to bind, switch the receiver off, then switch Tx20S on followed by the receiver.

Speed / Throttle Knob

The throttle control is low-off with no centre-click and operates R/C channel 1. Off/Stop is at the fully counter-clockwise rotation (left/CCW) of the knob and speed increases at the knob is rotated clockwise (right/CW).

Direction Knob

The direction control has a centre-click and operates R/C channel 3. It is typically used to control a servo connected to the loco reversing gear. If used with a receiver that has built-in ESC, the receiver must be configured for 'low off', full-range motor control.

Bind Button

Note: holding the bind button for longer than 20 seconds will result in strange things happening (see Calibration).

If a receiver has not previously been bound, it has to be 'paired' with the transmitter. Binding is only required once per receiver.

  1. Put your receiver into bind mode (if a Deltang Rx4 or Rx6 receiver, switch it on and wait for the LED to flash fast).
  2. Press and hold the bind push button on the transmitter.
  3. Switch the transmitter on by pushing the power button and then release the bind button.
  4. Binding is complete when the receiver LED stops flashing.

The bind button also operates R/C channel 5 and this can be used to control another servo - e.g. for operating a steam whistle.

Deltang Receiver Programming

You need to refer to the receiver's programming instructions for details of the available functions and the programming sequence to modify the functions.

The universal method of putting Deltang receivers into programming mode requires R/C channels 2 and 4. These are not available on Tx20S so the ‘SOS’ method must be used which works only on Rx6 receivers.

To Enter Programming Mode:
  1. Centre the direction knob
  2. Switch the Tx and Rx on and wait for the Rx LED to stay on solid; you should now have normal control of the model
  3. Wait at least 5 seconds without touching any controls
  4. Tap out the morse code ‘SOS’ on the bind button (… --- …)
    • dots (…) will be a quick press of the button and must be less than 0.7 seconds in duration
    • dashes (---) must be greater than 0.7 seconds and shorter than 5 seconds – 2 seconds is a reliable time
    • the time between each dot or dash must be less than 5 seconds
  5. If the SOS pattern is recognised, the Rx LED will display a repeating single-flash (1-flash pause and repeat)
  6. If you do not get the 1-flash, go back to step 3 and repeat the SOS
  7. Switch the Rx off at any time to abort
To make changes to receiver settings:

One programming change requires up to five choices to be made. These are called 'levels' and each has several options. They are documented in the programming table which is on the Deltang web site (go there or follow the link from the Micron R/C web page for a particular receiver). Completion of a programming change exits programming mode and requires the SOS sequence to be entered again for the next change.

You have to remember which level you are changing and the repeating LED flashes display the current option for that level. It is a good idea to write the programming sequence on a piece of scrap paper and cross off each digit as it is entered. You always start at level 1. For example, the first choice is the Menu number (programming group). The first option (1-flash) is for changing 'H' outputs, the second (2-flash) is Menu 2 to change P outputs for servos, 3-flash is for Menu 3 to change P outputs for on/off switching, etc. Refer to the Programming Table for your receiver to find the number of options and what they change. Each level is in a separate column, 1 to 5 left to right.

For example, to configure a Rx6 receiver output P4 to switch on (3.3V) when channel 3 is high (direction knob Fwd/CW), the programming sequence is 3,4,1,3,3, where:

3 = Menu 3
4 = P4
1 = momentary on/off
3 = R/C channel 3
3 = output idle 0V, 3.3V when channel is high (direction Fwd/CW)

The general procedure for entering a programming sequence is, for each level:

  • rotate the direction knob Rev/CCW and back to centre to increment the Rx LED flash count (called NO choices in the Deltang documentation); repeat this until the Rx LED is showing the correct flash count for the programming level
  • rotate the direction knob Fwd/CW and back to centre to accept the current flash count for the current level (called a YES choice in Deltang documentation) and move on to the next level in the programming sequence

When you make a choice with the direction knob (Fwd or Rev), the Rx LED will briefly flash rapidly and then the LED will:

  • direction knob Fwd/CW: display the current flash count for the next programming level or light solid when the end of the programming sequence is reached
  • direction knob Rev/CCW: display the next flash count for the current level; each programming level has a maximum flash count after which the flash count returns to 1 with another Rev/CCW movement of the direction knob

Changes are saved automatically when the Rx LED lights solid at the end of a programming sequence. If a mistake is made mid way through a sequence, switch the Rx off to abort.

Repeat the above steps for each program function that you wish to alter.

For example, to set the ESC output (the first if the receiver has multiple ESC) to respond to full range throttle on channel 1 and direction control on channel 3, the programme sequence is 1,1,2,1,3:

  • Enter programming mode
  • Rx LED displays 1-flash, direction knob Fwd/CW to accept
  • Rx LED displays 1-flash, direction knob Fwd/CW to accept
  • If rx LED does not display 2-flash, rotate direction knob Rev/CCW until it does, then direction knob Fwd/CW to accept
  • If Rx LED does not display 1-flash, rotate direction knob Rev/CCW until it does, then direction knob Fwd/CW to accept
  • If Rx LED does not display 3-flash, rotate direction knob Rev/CCW until it does, then direction knob Fwd/CW to accept
  • Rx LED lights solid


All ready-to-use transmitters are calibrated as the final manufacturing step. This sets the throttle control centre position and normally only needs to be done once. If you suspect that the throttle control is not operating correctly or you have replaced any of the internal components (e.g. throttle potentiometer), your transmitter may need calibration.

If the bind button has been inadvertently held down for longer than 20 seconds, the previously stored calibration data will have been overwritten and you could find that the throttle control behaves strangely.

To perform calibration:

  • Centre the throttle knob (white mark pointing toward the top of the Tx)
  • Centre the direction knob
  • Switch the Tx on
  • Within 60 seconds, press and hold the bind button
  • After 20 seconds, the Tx LED will go off
  • Release the bind button, the Tx LED come back on
The throttle control centre position is now calibrated.

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