Bachmann Optical? chuff sensors

  • Thread starter Neil Robinson
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Neil Robinson

Neil Robinson

Registered
24 Oct 2009
9,288
8
N W Leicestershire
More specifically those fitted to the 2-6-6-2 Mallet tank.

I'm in the process of rewiring a DCC installation and fitting a Phoenix P8 sound unit to one of these.
I'm sorely tempted to ditch the Bachmann main board
The only thing stopping me is my lack of knowledge on the chuff sensors.
Each has four wires labelled Tx+ Tx- Rx+ and Rx- If it helps the Rx+ checks out as connected to Bachmann's output terminal on the board with both Rx- and Tx- to Bachmann's GND

I've emailed Phoenix, I've found them very helpful in the past but I'd like to progress the project this weekend if possible.
 
PhilP

PhilP

G Scale, 7/8th's, Electronics
5 Jun 2013
22,244
96
Tamworth, Staffs.
Without input from either Bachmann or Phoenix, I would be tempted to keep the main board.. Feed it from a polarity switched relay fed from the decoder rails.
That way you keep all Bachmann's wiring etc for lights.. The two sensors come out on the large connector at the end of the board, in effect they are switched to ground. - I assume you have the Bachmann schematics?

http://www.bachmanntrains.com/home-usa/dwg/dwgs/82894.pdf
 
John S

John S

Registered
5 Nov 2017
507
33
Exeter, Devon, UK
Bachmann Optical Sensor, (no different from a bog standard optical sensor from evilbay) the four wires to the sensor: brown, red, orange, and yellow.
The brown and red wires connect to the anode and cathode of an IR LED.
The orange and yellow wires connect to the collector and emitter of a photo transistor.
As per the TX RX combination mentioned in post 1

The IR LED is on continuously when power is applied and light is reflected back into the photo transistor.
When the IR light hits the photo transistor, it conducts and takes the chuff output to ground.
When the light does not hit the photo transistor, it does not conduct and the chuff output goes to +5 volts.

Try this link for an explanation and a work round: Phoenix Sound P8 in a Bachmann K27 » Ottawa Valley Garden Railway Society
 
Last edited:
Neil Robinson

Neil Robinson

Registered
24 Oct 2009
9,288
8
N W Leicestershire
Bachmann Optical Sensor, (no different from a bog standard optical sensor from evilbay) the four wires to the sensor: brown, red, orange, and yellow.
The brown and red wires connect to the anode and cathode of an IR LED.
The orange and yellow wires connect to the collector and emitter of a photo transistor.
As per the TX RX combination mentioned in post 1

The IR LED is on continuously when power is applied and light is reflected back into the photo transistor.
When the IR light hits the photo transistor, it conducts and takes the chuff output to ground.
When the light does not hit the photo transistor, it does not conduct and the chuff output goes to +5 volts.

Try this link for an explanation and a work round: Phoenix Sound P8 in a Bachmann K27 » Ottawa Valley Garden Railway Society
Thanks John,
I suspected that the sensors were of that type.
My uncertainty is down to the knowledge that the sensor power circuit in Phoenix's information on the K27 is specific to the K27 as that loco's electronics defies some conventions. Apparently Bachmann made modifications to the later locos.
 
Tony Walsham

Tony Walsham

Manufacturer of RCS Radio Control.
25 Oct 2009
2,092
2
Casino, NSW
As far as I know it was only the K27 that required fitting a transistor as a signal inverter. to convert the chuff signal from 5+ to low output.
Later Spectrum locos were changed to be low output such that all regular sound systems could use them.