Table of Contents
MGV77 Interface for turnout coils and illumination
how it looks like
Features
- 8 outputs each 0.5A max .
- Opto-coupler isolation between Loconet and outputs.
- Simple connection to MGV50
- For switching turnout coils.
- Also to be used as light switch.
Description
First question may is: why should we use interface and MGV50 LocoNet, since there are turnout decoders available that connects straight to the rails, and will be commanded by either Motorola or DCC commands.
There is a simple argument for that.
If you ever used turnout drives , commanded with Mot. or DCC, you also will have seen that everytime you, or in our case Rocrail, switches a turnout, you can see that light in Locs are flac=shing, due to the sudden drain of power from the rails. And the longer the connection between central station and the turnout decoder is, the lower the available power for that turnout will be. Since we did not like all these signals, we prefer a separate supply for turnouts. This supply is even not used for anything esle on the railroad track i.e. lights etc.
In that case it is better and far more reliable to send commands for tuernouts and signs by means of LocoNet.
The standard LocoIo module MGV50 has limited capacity for switching outputs.
GCA50 can only deliver 5 Volts and max 25 mA on each output which is suitable enough for connecting LEDs and small relays.
Turnouts and arm signs with coils use much more power, in voltage and current, than MGV50 is capable to supply.
For that purpose the first available interface is MGV77.
It is a good interface for using with low current turnout drives, mostly in N scale systems.
On one side (top on picture) it is connected with MGV50, by means of 10 wire cable.
At the bottom screw terminals 8 outputs (4 turnouts) are to be connected.
An addional power connection needs to be connected to transformer/adapter 16V ac or dc, or to rail power.
Optocouplers on board will separate the Loconet circuit from the addional power.
This board also can be used to switch lights on your railroad setup.
It is to be considered, that max load of the printed circuit can not exceed 1Amp.
If more than 300 mA is to supplied by the circuit, the Fuse F1 has to be adapted.
For heavier loads, refer to MGV76 (double coil system) or MGV125 (single coil system).
Files for d.i.y.
The schematics version 1.3 |
The PCBlayouts version 1.3 + parts placement |
Bill of materials |
Connections MGV77 |
Connection to MGV50
refer to: Connection cable MGV50
Known current of switch coils
For detailed info about different makes of turnout solenoids please refer to this page
Instructions for controlling the GCA77 (e.g. for turnout coils)
The GCA77 must be activated with positive pulses.
This means that 5V must be switched on at one input and switched off again shortly afterwards.
There is no function on the GCA77 itself to ensure switching off.
Standard turnout decoders usually - there are exceptions - do not have such a function either.
Shutdowns are done by software in central units or programs, which activate the coils and deactivate them after about 200ms.
With a GCA77 connected to a GCA50, this can be done much more safely by the GCA50 hardware itself.
Assuming GCA77 is connected to J5 from GCA50 and the switches have address 1 to 4.
In this case, the example below should be programmed for port 1 to 8.
IMPORTANT:
Always briefly disconnect the power supply to a GCA50 after programming it
Another question is the start of the LocoNet system. Under normal circumstances all switches will react a little bit. The best way to avoid this is to remove resistor group RP1 or RP2 depending on the connector J5 or J6 used for GCA77.
Using GCA77 for permanent switching applications (e.g. motors, lighting with leds/bulbs)
GCA77 not only can be used for pulse switching coils of turnouts (with short pulses, see above). Also permanent switching on and off gadgets, e.g. leds, bulbs, or motors is possible.
For those applications GCA50 / CAN-GC2 / GCA_PI02 have to be programmed with option switch (not pulse).
Please note that max load of the printed circuit can not exceed 1Amp.
If more than 300 mA is to supplied by the circuit, the Fuse F1 has to be adapted.
Note that when programming in the easy setup menu of the GCA50, the switching outputs are on by default.
If it is desired that the outputs are off when the GCA50 is turned on, the I/O menu must be used:
For more details see LocoIO Dialog Tab 'I/O'
For more details see CAN-GC2 Universal 16-port I/O node for CANBUS
Example of RocNet GCA_PI02 or GCA_PI03 settings for GCA77 | |
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Port 1-8 are set to control 8 switching outputs of GCA77. |
For more details see GCA_PI02 32 I/O I2C board for Raspberry Pi. - Address selection