[SOLVED] Looking for a circuit which can reverse polarity using just one control input line

[level20peon]

You lead, I followed and bought this one. A flyback diode is a good idea!
Is there anything I have to consider when wiring the relay (not considering the diode) ? Do I have to connect A1 AND A2 to my control signal?

 

[betwixt]

Good choice, you could use a smaller one but there is no harm in using one with a higher than necessary rating.

Yes, you do have to connect A1 and A2, they are the pins that need the diode across them and are fed your control signal.
The mechanism connects to pins 11 and 21.
The power for the mechanism connects to pins 12 and 14.
You link pin 14 to pin 22 and pin 12 to 24.

Brian.

 

[level20peon]

I tested the relay and it doesn't work as intended. Apparently, the control signal is too weak to flip the relay, although it outputs around 6V. So I tried to use a TIP120 (I have no other spare transistor or MOSFET right now), but it also won't really work with that. Either the relay is always on, or always off (I tried low-side switching and high-side switching). I am at a loss, maybe there is a relay which requires less power to flip, I can't really determine which value at farnell represents the power requirement for switching. Or maybe I need another transistor. Or maybe I am just too stupid to wire the transistor correctly.
Do you have any suggestions?

 

[KlausST]

Hi,

I'm sorry to say that... but the text is almost useless. Impossible to find an issue or to find a solution.

Why don't you post your schematic and we all can discuss about it?
With all important informations like voltages, currents, device types...


Klaus

 

[betwixt]

Most importantly, where does the control voltage come from?

Brian.

 

[D.A.(Tony)Stewart]

Use output to control relay or High Side power switch using 3V logic and supply. Logic voltage = minimum input V+ swing to guarantee Hysteresis e.g. 3~3.3V

Signal clamps must use Schottky diodes to protect CMOS. R values can be scaled up if desired.




It also converts the bipolar input voltage to the supply voltage level unipolar logic using clamp Sch. diodes.

THe output toggles on either input edge.
Input edges must be clean or filtered.

https://www.falstad.com/circuit/circuitjs.html?

 

[betwixt]

Good solution Tony - but not to this problem!

The idea here is to reverse the supply voltage to a magnetic shutter module using a single on/off control voltage. It is complicated by needing to work from supplies between 3.3V and 12V and drive a coil of ~45 Ohms (~270mA).

As I see the thread at the moment, Level20peon has settled on using 12V using a DPDT relay wired as a crossover switch but they can't control the coil properly. They have tried using a TIP120 driver without success but we are not sure how they connected it. The TIP120 is a bad choice if the control voltage is low because Vbe can be as high as 2.5V (it's a Darlington) but until we know excatly what provides the control voltage it's difficult to advise.

Brian.

 

[D.A.(Tony)Stewart]

A magnetic shutter with no spring? Pulse mode Bipolar output? or latched output?

GLad you understand the "spec" , I didn't

 

[betwixt]

It's a mechanism that moves an IR filter in or out of an optical path and has a camera style mount.

The adverts show no specification whatsoever but it appears to have no 'return' spring, it doesn't appear to have anything at all to keep the mechanism in place except the current through the coil. In other words, without a steady current it could adopt any position or be loose. I am a little suspicious that there may be more to this mechanism than we know, the coil dissipates about 3.2W of heat if left energized and in an optical application, that would be likely to cause undesirable expansion in the lens system.

Brian.

 

[level20peon]

Hi,

I'm sorry to say that... but the text is almost useless. Impossible to find an issue or to find a solution.

Why don't you post your schematic and we all can discuss about it?
With all important informations like voltages, currents, device types...


Klaus

You are totally right, no need to be sorry for that. It was late and I was lost. After a good night of sleep, I solved the problem.

Good solution Tony - but not to this problem!

The idea here is to reverse the supply voltage to a magnetic shutter module using a single on/off control voltage. It is complicated by needing to work from supplies between 3.3V and 12V and drive a coil of ~45 Ohms (~270mA).

As I see the thread at the moment, Level20peon has settled on using 12V using a DPDT relay wired as a crossover switch but they can't control the coil properly. They have tried using a TIP120 driver without success but we are not sure how they connected it. The TIP120 is a bad choice if the control voltage is low because Vbe can be as high as 2.5V (it's a Darlington) but until we know excatly what provides the control voltage it's difficult to advise.

Brian.

The voltage sufficed.

As it turned out, the solder of the control line became lose, so the signal didn't put much power through. I fixed that and now everything works as intended (I need the driver nonetheless).

Thank you all for you input and patience, you were really helpful and saved my weekend. Tank you!