Switching anode/cathode

Thread Starter

coder

Joined Jun 7, 2006
2
Hi,

I'm working on a prototype which uses a latching solenoid (coil) to move an armature. To change between positions I need to reverse the anode/cathode of the coil and supply 3V for 100ms. My problem is that I write software and don't get into hardware much, so although it seems simple in concept I'm not sure how to design a circuit that allows me to control, via two IO pins, the solenoid. Originally I was thinking some kind of electronic DPDT switch but, guess what, in order to control it I need to reverse the anode/cathode! (kinda an infinite loop for me)

Any help would be appreciated.
 

Papabravo

Joined Feb 24, 2006
12,767
Originally posted by coder@Jun 7 2006, 02:16 PM
Hi,

I'm working on a prototype which uses a latching solenoid (coil) to move an armature. To change between positions I need to reverse the anode/cathode of the coil and supply 3V for 100ms. My problem is that I write software and don't get into hardware much, so although it seems simple in concept I'm not sure how to design a circuit that allows me to control, via two IO pins, the solenoid. Originally I was thinking some kind of electronic DPDT switch but, guess what, in order to control it I need to reverse the anode/cathode! (kinda an infinite loop for me)

Any help would be appreciated.
[post=17603]Quoted post[/post]​
A diagram of your starting point would be helpful.
 

billbehen

Joined May 10, 2006
39
Originally posted by Papabravo@Jun 7 2006, 03:25 PM
A diagram of your starting point would be helpful.
[post=17609]Quoted post[/post]​

Sounds like a DPDT relay and a couple of diodes would do the trick -- a sort of backwards rectifier, that would conduct current one way through the solenoid when the relay was thrown one way, and the other when it was thrown the other! The DP aspect of the relay would let you reverse both connections to the solenoid at the same time; the diodes would prevent a short circuit.
 

Papabravo

Joined Feb 24, 2006
12,767
Originally posted by billbehen@Jun 7 2006, 04:57 PM
Sounds like a DPDT relay and a couple of diodes would do the trick -- a sort of backwards rectifier, that would conduct current one way through the solenoid when the relay was thrown one way, and the other when it was thrown the other! The DP aspect of the relay would let you reverse both connections to the solenoid at the same time; the diodes would prevent a short circuit.
[post=17610]Quoted post[/post]​
A picture would be worth several more paragraphs anyway.
 

Thread Starter

coder

Joined Jun 7, 2006
2
Thanks Ron. I read through the thread which turned me onto mosfet drivers. After looking at a few schematics I came up with the attached schematic. AFAIK it should work, although I noticed one schematic had diodes to protect from under/over voltage (from the motor they were driving).
 

Ron H

Joined Apr 14, 2005
7,014
Originally posted by coder@Jun 8 2006, 07:49 AM
Thanks Ron.  I read through the thread which turned me onto mosfet drivers.  After looking at a few schematics I came up with the attached schematic.  AFAIK it should work, although I noticed one schematic had diodes to protect from under/over voltage (from the motor they were driving).
[post=17635]Quoted post[/post]​
Notice that the output resistance is around 7-10 ohms, so your series resistor should be changed to 47 ohms. Also, the chip will burn up if you accidentally leave it on for too long. I don't know if 100ms is too long. :(
EDIT: power dissipation shouldn't be a problem with 200mA and 100ms. I was using 400mA when I made that conclusion.
 
Top