# Controlling Multiple Solenoids by varying voltage

#### ofu71

Joined Aug 5, 2014
1
I want to control multiple (15 - 20) solenoids by using a common single variable resistor. For example solenoid 1 will energize if control voltage is between 1 and 1.25 volts only. Solenoid 2 will energize if control voltage is between 1.5 and 1.75 volts only, etc. Solenoids will be parallel off a single 12 -24 volt line, control circuitry will be parallel off a single 0 - 12 volt line.

Joined Jul 18, 2013
22,641
You may have a problem with the coil hysteresis, especially DC solenoids.
And where are you going to obtain solenoids with those characteristics?
The other way is possibly to use LM311's for each circuit.
Max.

#### alfacliff

Joined Dec 13, 2013
2,458
sounds like the method yaesu uses for band switching to antenna tuner, different voltages for each band.

#### Dodgydave

Joined Jun 22, 2012
9,916
I would use an LM3914 set up to 0.25v per comparator, or use a series of separate opamp comparators using an LM324, each set at the respective trigger voltage, use transistors to drive the solenoids.

Like this battery monitor, as your voltage rises or decreases each op amp switches on/off.

#### KMoffett

Joined Dec 19, 2007
2,918
Looks like a job for a microcontroller with an analog input and an appropriate number of outputs (PICAXE40X2), plus driver chips with the needed number of channels (ULN2803?).
What's the current requirement for the solenoids?

Ken

#### Alec_t

Joined Sep 17, 2013
11,981
I'd try the dodgydave approach. Two cascaded LM3914s with 20 pull-up resistors, driving 20 P-channel FETs for high-side switching of the relays.

#### Johann

Joined Nov 27, 2006
190
I'd try the dodgydave approach. Two cascaded LM3914s with 20 pull-up resistors, driving 20 P-channel FETs for high-side switching of the relays.
LM 3914 is a winner and should work very well for this project.

#### crutschow

Joined Mar 14, 2008
26,740
LM 3914 is a winner and should work very well for this project.
I third the motion.

Note: Be sure each solenoid has a reverse diode across the coil for transient suppression.