NLMS - Dutch ModelRailroad -

High current switch decoder.

Here I describe a switch decoder from the same type as the Marklin K80. The same parts are used, as with high current Darlington transistors. This was the first switch decoder I build and since there was a lot of room left on the circuit board, I decided to make two decoders on one circuit board the next time.

The decoder is build around the Motorola 145027 chip. The address is selected with a 8 position dip switch. This dip switch controls the Motorola MC145027 inputs. The dip switch can be replaced with jumpers, like the ones used in computers, or even soldered directly to the Motorola MC145027 chip. However the address can not be changed.

I also added a few LED's in the circuit to aid in connecting and troubleshooting. When the digital power from the booster is connected correctly, the green LED lights up. When the digital signal is present then the red LED lights up. When the switch decoder receives a command, the yellow LED will flash.

Normaly the Darlington transistors need cooling but since the current flowing trough the Darlington is from a short time, there is no need for this.

Click here for the schematic: hi power switch decoder

Click here for the parts list: hi power switch decoder

Here we see the entire circuit board. The dip switch is red. The dip switch is used for selecting the address. The connectors to the power and switches are in blue.
Here we see the Darlington transistors. The other track switch decoders, on the red circuit boards, use another way of sending power to the track switches.
Here a look at the addition. It is a small diagnostic circuit. The red and green LED indicates if the polarity is connected correctly and if there is a digital signal present. The yellow LED indicates the decoder receives a command.
Here the circuit board from behind.

This page is last updated on 15 July 2012

NLMS - Dutch ModelRailroad -