angie
Hi Mr Deb,
No there is only one relay per detector driver board. The output from one relay is connected to the four adjacent block detector driver boards. i.e Two ahead east bound and two ahead westbound. For setting the red against a switch point I fake an occupancy so that the correct aspects are propogated behind a stopped train. The signal in front of the train has to show approach medium divert i.e. flashing yellow. As to the cost of a relay, I have yet to pay more than a dollar for one. The ones I use I bought at an electronic surplus store. The cost is about 90 cents for a SPST type. I agree transistors are cheap but in the envirnment that they are being used i.e. electrical noise, electro mechanical interfacing, the extra components reqired to protect them brought the cost over and above the simple relay. Also my 25 year old ´little´ home project was meant to be just that and anyone was to be able to build, configure, maintain and trouble shoot it without having a degree in electronics. I tried an emitter follower circuit instead of a relay only to find that a transistor failure propogated its condition not only to its neighboring controlers but to its own detector. It was a mess. The relay offers TOTAL isolation and any problem is easilz isolated to a board. The board can easily be unpluged and replaced within seconds. AND, since I adopted this philosphy I have yet to have a failure on my layouts.
Today a self builder can build a PC board for about ten dollars. The two signals run about 9 dollars each. There is of course a one time overhead but even that can be made from materials on hand. One would require a power supply and a home made card rack. I use an old throttle to run my system and the rack is made of timber. One card slot in the rack is reserved for conditioning the power. I use a commercial voltage regulator. The cost of that item was 20 cents.
The detector I use is a Twin T type. It was invented by Lynn Westcot in the 50s. It is a bidirectional current sensor which in its simplest form drives a lamp or relay. It requires two transistors and two resistors. (I seem to remember , I am not at home right now, hence the choppy grammar. I am using a cyrilic keyboard). The cost of these components, which by the way, includes the reed relay is about 3 dollars 50 cents. I also added an inverter and debouncer circuit to prevent chatter. The detector does not require power to be applied to the track to work. So if you are working with DC and a section without power has an engine or car with conductive paint one some axles the detector will still do its job and trigger its relay. I suggest you check on the net. If you cant find anything Ill put something together for you.
Looking forward to this
Pete