Open Decoder Schematics

Posted on Feb 6, 2014

This software was written for this hardware. Therefore the pin allocation of the Atmel Attiny2313 in this curciut corresponds to the orginal of So the software will run on both hardware platforms. Important note: The processor AT90S2313 requires an external reset generator (TL7705) as well as an external quartz. With the processor ATtiny2313 these parts aren`t needed

Open Decoder Schematics
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(but you will find them in the diagram as an option). If the quartz is omitted, the Attiny must be set for 8MHz and internal oscillator and the source must be compiled for 8MHz as well. So with the ATtiny2313 you can leave out: C4, C5, C6, C7, R3, R4, IC3 and Q1. At X2 the input voltage of the external power pack is fed in (approx. 15V); Polarity and type of current doesn`t matter: a transformer for model railways, a plug power pack or the DCC signal itself can be used. The input voltage is rectified and by means of the usual 7805 limited to 5V for the supply of the processor. The idle current amounts to approx. 20mA. Note: I stated that some magnetic turnout drives from Roco need up to 15V to operate properly; In this case supply voltage is to be increased by the voltage drops at the rectifiers and output drivers to 16V~ or 18V=. To X1 the DCC signal is attached. This is separated by means of an opto coupler from the voltage supply of the decoder. The opto coupler provides a troublefree operation even on large layouts. Usable as opto coupler is 6N136 or 6N137 or even 4N25. When using the 6N137 the pin 7 (enable) must be connected to pin 8 (this is not in the layout of the pcbs V1. 1). The 4N25 (or its derivatives) must be equipped in such a way, that pin 1 of the 4N25 coresponds to pin 2 of the layout. The 4N25 is slow, in particular the recovery time is relatively long. Therefore the pullup at the output should be...

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