Acknowledge Detector Variant 1
This circuit can be used for detection of Basic Acknowledgments from
a Digital Command Control (DCC) Decoder following
NMRA
RP9.2.3 (Service Mode). It can be used together with (or to modify)
DCC-MB
or TMWDCC.
(ACKDET01.GIF)
Notes
- You can invert the output signal by exchanging the inputs of IC1A (simply
exchange R2, R3 and C1, C2)
- If you don´t need an optocoupler between the track and the PC remove
R1 and connect IC1A,2 direct to U10A,1
- I have tested this circuit with a Digitrax DH84G Decoder and a
current-limiting-resistor (Resistor R1 of the TMW4 board) of 120Ohms.
The Voltage at the track has been approximately 15V. It drops to approximately 3V
when the decoder gives the acknowledge pulse. A pulse of approximately 35mV
and 2.5ms can then be measured over R3. This gives an high-level-pulse
of approximately 2ms at the input of U10A. With TMWDCC (Version 1.11) I have
successfully read back values form the decoder.
- The calculated DC-input-levels of the comparator IC1A at different
track currents are:
| Track Current / A |
level at pin 5 / V |
level at pin 4 / V |
difference / mV |
| 0.000 |
0.0495 |
0.064 |
14 |
| 2.123 |
1.0396 |
1.051 |
11 |
| 3.191 |
1.5347 |
1.5449 |
10 |
ACKNOWLEDGE DETECTOR 2
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© 1997 by Martin Pischky (martin@pischky.de)
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