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Readme First
Just one initial note: All information presented on this page is a result
of ideas, and is not physically tested in practice. Any feedback is welcome,
please see the feedback form at the end of this page.
Using one external transformer
Often, a model railway transformer is already available; and it is a wise idea not to play with lethal voltages but use safe transformers built for use by children.
Here is a variant of the original schematic of my bogobox booster:
The schematic is also available as PDF-File.
Compare this alternative schematic with the original. If you just use
one transformer input, you do not need components L1, L2, D1, D3, and
connectors P5, P8. Connect P1 and P2 to your transformer of 15 - 18 V AC.
In case of a märklin trafo, connect P1 to yellow, and P2 to brown.
Ignore components R54, R55, P9 for the moment.
Using two external transformers
As explained on the first page, using only one AC input has the disadvantage that the filter capacitors C1 and C2 are recharged only every other halfwave of the AC cycle. Thus the output voltage ripple is high. Voltage ripple is reduced by using two antiphase AC inputs. So you need two separate transformers of equal rating.
Here is a variant of the original schematic of my bogobox booster:
The schematic is also available as PDF-File.
Connect P1 and P2 to your first transformer of 15 - 18 V AC.
Connect P5 and P8 to your second transformer.
In case of märklin trafos, connect P1 and P8 to yellow plugs, and P2 and P5
to brown plugs. To see whether the two transformers run at opposite phase
there are the two 16 V light bulbs L1 and L2 in series (you may alternatively
use one 32 V light bulb but this is hard to get). Light bulbs for house
illumination or loco headlights should do well (but check their voltage rating,
must be at least 16 V). If the two bulbs light brightly, all is in order.
If they remain dark, take the wall plug of one transformer and plug it in
again but the other way round (turned by 180 degree). Now the bulbs should light.
Ignore components R54, R55, P9 for the moment.
Feedback to the serial port
If software-based central units are used, for example DDL, they usually are able to monitor the serial port's DSR status line. An inactive line (zero or negative voltage) indicates normal operation, an active line (positive voltage) indicates a short circuit / overload condition.
This can be easily implemented if a relais is used for Rel51 that has
two switching contacts. One is used for switching the output, the other
one is now used to apply the appropriate voltage to the DSR line.
See the components R54, R55, P9 and contact Rel51 in the schematic:
The schematic is also available as PDF-File.
Keep in mind that at power on of the bogobox the relais Rel51 is initially in the off position. The computer may display this state as short circuit, but you should know that this is the normal power-on state and nothing to worry.
Connections to the serial port are then made as follows
9pin serial | bogobox
port |
7 RTS ------o-.
|
8 CTS ------o-'
1 DCD ------o not connected
4 DTR ------o not connected
6 DSR ------o--- to P9, DSR
9 RI ------o not connected
2 RxD ------o not connected
3 TxD ------o--- to P3, TxD
5 GND ------o--- to P4, GND
Also read the section about
Feedback to the serial port, part 2
Optocoupler Input
Under certain conditions it is a good idea to have the railway electrics
insulated from the computer electrics. This requires the use of an optocoupler
at the input. A possible implementation might look as follows:
The schematic is also available as PDF-File.
This schematic only shows the input part of the whole bogobox and hence is just an "appendix" to the original bogobox schematic. The components R1, R2, R3, R4, D5, D6 are wired differently, The components with a reference number of 90 and higher have been added. If unwanted, LEDs D5 and D6 can be omitted, then connect R1 to D91, and R2 to D92. For the moment igore connectors P9 and P10 and the relais contact.
The initial design had the feature that the output voltage is zero
(output turned off) if there is no input signal present, i. e. computer
is off or not connected. This is not the case any more for the optocoupler
input und thus renders this variant unsuitable for Selectrix or FMZ signals.
If nothing is connected to the input, the booster produces a negative
DC output. This may be acceptable for locos with märklin decoders as they
interprete negative DC as the general command to stop (as in front of a
signal). And you should not forget that a "GO" button (at connectors P51 and
P52) needs to be pressed first, before any output is switched on by the relais.
Feedback to the serial port, part 2
As already written before, if software-based central units are used, they may monitor the serial port's DSR status line. An inactive line (zero or negative voltage) indicates normal operation, an active line (positive voltage) indicates a short circuit / overload condition.
This can be easily implemented if a relais is used for Rel51 that has
two switching contacts. One is used for switching the output, the other
one is now used to apply the appropriate voltage to the DSR line.
The restriction now shall be to do this in an electrically insulated way.
See the components R54, R55, P9 and contact Rel51 in the schematic:
The schematic is also available as PDF-File.
The normal operating condition should be signalled with a negative voltage, but this is not available, so we leave the line open, which is interpreted as inactive by the computer's serial port. If a short occurs, a positive voltage must be signalled, which is available all the time from the RTS line, or available during track signal generation from the DTR line. Let us look at the one case where we take the RTS line at connection P10. If the bogobox relais is off, the computer gets positive voltage into DSR and interpretes this as short circuit. This might be misleading at the initial power on of the bogobox where we also have the relais in off state. In the other case we take the DTR line at connection P10. If the bogobox relais is off, the computer gets its own state reported back. So if the bogobox relais is off, and the computer is inactive, then DTR is negative, and also DSR is negative, so all seems fine to the computer. But if the bogobox relais is off, and the computer is active, then DTR is positive, thus also DSR is positive, and the computer receives a short circuit state. Now the computer responds by becoming inactive (DTR negative), which in turn makes DSR negative, and the computer receives the return to a normal booster state. You should decide yourself which logic is more appropriate for your application.
Note that this feedback wiring is not restricted to the optocoupler signal input. This feedback wiring can also be used with the original bogobox input circuit.
Connections to the serial port are then made as follows
9pin serial | bogobox
port |
7 RTS ------o--- to P10, RTS; only if DTR is not connected
8 CTS ------o not connected
1 DCD ------o not connected
4 DTR ------o--- to P10, DTR; only if RTS is not connected
6 DSR ------o--- to P9, DSR
9 RI ------o not connected
2 RxD ------o not connected
3 TxD ------o--- to P3, TxD
5 GND ------o--- to P4, GND
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last update: 2003-01-29;
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