I have a little Z-guage model railway I control via a Velleman K8055 USB interface board, using 5V sealed reed relays I got from my local Maplins (http://www.maplin.co.uk/sealed-reed-relays-2605
) to trigger the turnouts. Clearly, I could use this set-up with my raspi (someone has already reported success in porting the Linux driver, see http://forum.velleman.eu/viewtopic.php?f=12&t=7838
), but it seems silly using an interface board three times the size of the raspi when I should be able to do it directly from the GPIO (plus a small breadboard, in both cases). Unfortunately while the relays are low drain (they have 500 Ohm impedance) they need at least 3.8V to trigger. Can someone suggest a simple circuit with commonly-available components I could use to drive these relays, please?
Even better, to allow me to control a turnout with one GPIO line, could someone help me with a circuit that would briefly energise one relay on the rising edge of the GPIO line, and do the same for a different relay on a falling pulse? This would also reduce the danger of burning out the turnout coils by activating them too long, or activating both coils at once! The 'normal' way these turnouts are activated is by pressing a a switch that temporarily connects the 10VAC output from the transformer unit to the appropriate coil of the turnout.