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[on:]

This pump has a run/stop switch pins that can be controlled by the dipital output of Arduino. The switch gets closed (RUN) when the digital value of the port is LOW.  This means than when the Arduino is disconnected the switch is closed and the Pump runs. 

How can I make the connections for the Pump not running when Arduino is disconnected?

[Reply #1 on:]

A pullup resistor?

[Reply #2 on:]

I  have this  same  pump at work  so I  know what you  are  talking about.  Easy way is to  use a  relay, specifically a DPST relay,  apply 12v to the common pin,  connect  the NC  pin to  the pump,   the no  can be  left floating,  connect the coil  to the  arduino (ideally via something to  isolate the inputs  on the arduino from the  back emf).  When  arduino is  connected and the coil is activated  no 12v,  pump runs.  disconnect  arduino the  relay  goes off  and  supplies 12v  to the  pump,  pump turns off.  Additionally,  if  you  dint activate the coil,  the pump  remains  off.

 Sorry  for any typos  or  what not,  sent  using my phone.

[Reply #3 on:]

I  have this  same  pump at work  so I  know what you  are  talking about.  Easy way is to  use a  relay, specifically a DPST relay,  apply 12v to the common pin,  connect  the NC  pin to  the pump,   the no  can be  left floating,  connect the coil  to the  arduino (ideally via something to  isolate the inputs  on the arduino from the  back emf).  When  arduino is  connected and the coil is activated  no 12v,  pump runs.  disconnect  arduino the  relay  goes off  and  supplies 12v  to the  pump,  pump turns off.  Additionally,  if  you  dint activate the coil,  the pump  remains  off.

 Sorry  for any typos  or  what not,  sent  using my phone.

ACtually, with the minipuls3, you just have to short the two pins on the motor start/stop to start the motor and open them to stop it. This is even easier because you can just use a simple NPN to short them. Remember to control the motor from the back, the pump has to be stopped via the front panel.

[Reply #4 on:]

Thanks Pedro,

I am sure that with a NPN or a delay it will work, but following the instrument guide it should work with a TTL signal.  Which is much more simple.  In fact it works perfectly with the direct connexion to a digital Output of the Arduino, but the unique problem is that of been ON when port output is LOW, even when the Arduino is disconnected.

I am sorry but I do not know what is a Pullup Resistor.

[Reply #5 on:]

Thanks Pedro,

I am sure that with a NPN or a delay it will work, but following the instrument guide it should work with a TTL signal.  Which is much more simple.  In fact it works perfectly with the direct connexion to a digital Output of the Arduino, but the unique problem is that of been ON when port output is LOW, even when the Arduino is disconnected.

I am sorry but I do not know what is a Pullup Resistor.

It does work with a TTL signal, just not the way you want it to. It is designed this way so that with nothing attached the front buttons control the device (having two sources of control could be a disaster in a work environment). So the problem is to get the device to behave how you want. Somehow you HAVE to apply >2V to that pin when the arduino disconnects. The easiest would be with a relay, like I said. There is no way around having to use extra hardware, unless you somehow dump the devices firmware and hexedit it and reflash the pump. 4

You could use a 4N32 optical isolator, a 5V supply, and a relay. Done, that should be all you need.