SIMPLE ELECTRONICS HELP PLEASE?

[tony168]

I have a simple ON/OFF passive magnetic switch used as a sensor on the rotorhead of an autogyro that I want to connect to MGL's ROTOR-1 tacho guage.

Having emailed MGL I'm still a bit in the dark as to how I wire the system up. Their reply is as below:

One wire from your switch goes to ground (negative of the battery).
The other wire goes to the ROTOR-1 RPM input. This wire also gets a resistor going to 12V.
The resistor "pulls" the line to 12V when the switch is open.

Presumably the spec of the resistor is pretty critical. Does anyone know how to work the optimum value of this component out please?
(Wish I'd paid more attention in physics class now !)

Thanks in advance Tony

[Steve Brown]

Why not use the Hall effect sensor suggested on page 18 / Section 11.8 of the manual?

http://www.mglavionics.com/Rotor1.pdf

May be better than a simple (reed?) switch which may bounce.

Pull up/down resistors are common but hard to give a ohm value/wattage because the max closed current/ open circuit voltage allowed would need to be known - wouldnt want to risk damaging the unit - particularly as it has a 5volt rather than 12 v terminal.

Or get a specific wiring diagram and resistor value from MGL to be sure.

Hope that helps
Steve

[Clive Richards]

Hi tony
I would try a high value of resistor to start with ie 12000 ohm will give you about 1 ma, reed switch should be ok with that. terminal input is shown as 100 v pp so no problem with 12 v

Clive

[tony168]

Thanks, Steve & Clive.
Much obliged.