This article is from before 2012

DCC - 2 - Switch & signal decoders

This article is about self made switch and signal decoders, all based on the Motorola protocol.

To digitally operate my switches I am using two types of decoders, a low current switch decoder and a high current switch decoder.

For light signals I also use two types of signal decoders, which can only be used with the MRDirect system. One decoder is for a 2 light signal and the other one is for a 3 light signal.

The high current switch decoder

Here I describe a switch decoder of the same type as the Marklin K80. The same components are used, so with high power Darlington transistors. This was the first switch decoder that I built and since there was a lot of printed circuit board space left I came up with the idea to build the next printed circuit board with two decoders.

The decoder works with the Motorola MC145027 chip. The address is set with a dip switch, which has 8 positions. The inputs of the Motorola MC145027 are controlled via this dip switch. The dip switch can also be replaced by a number of jumpers as used in computers, or possibly soldered directly to the Motorola MC145027, but then the address can no longer be changed.

I also added a number of LEDs that make connecting and possibly troubleshooting easier. If the power supply is connected correctly, the digital voltage of the booster, then the green LED lights up. If the digital signal is present then the red LED lights up. Only when the switch decoder is called at its address does the yellow LED flash.

Normally the Darlington transistors need heatsinks, but since there is only a short current flow this is not necessary here.

Here is a look at the entire circuit board. The dip switch is red. This sets the address of the decoder. The connections to the switches and the power supply are blue.

Here is a look at the Darlington transistors. The other, red printed circuit boards, no longer have these but use a different way of switching coil control.

Here is a self-built adjustment. It concerns an aid in troubleshooting. The red and green LED are as an indication whether the polarity is connected correctly and whether a digital signal is present. The yellow LED comes on when the decoder in question is addressed by the central unit.

Here is the printed circuit board from below.

The low current switch decoder

Hier komt binnenkort de beschrijving van de laag vermogen wissel decoder.

Hier komt binnenkort het schema.

Hier komt binnenkort de onderdelen lijst.

Here a double switch decoder like the yellow print with the Darlington’s. However without the expensive Darlington’s. Otherwise the principle is the same. But now 8 switches on 1 print.

Here is a look at the dip switches that set the address of the decoder. It can be made cheaper if you just permanently solder the addresses with a wire bridge, and of course you can also leave out the auxiliary circuit with the LEDs.

Here is the printed circuit board from below.

The 2 and 3 light signal decoders

Description coming soon

A signal decoder. The differences with the switch decoder are another way of voltage regulation, instead of a zener diode. The MC 145027 is connected in a different way and so the output is different, because a light signal must remain on and cannot receive a momentary signal. This circuit was designed by Mr. A. de Heer.

A double signal decoder for 4 x a three light signal. A special software command is needed to control this. Can only be used with the MRDirect system.

A double signal decoder for 8 x a two light signal. A special software command is needed to control this. Can only be used with the MRDirect system.