Voltage-sensing switch

Thread Starter

dsalvail

Joined Mar 1, 2021
3
Good day everyone.

This question from a (medical) newbie (use simple words in short sentences, please):

I'm monitoring animals with lowering blood pressure and need to automatically start 110V infusion pumps to increase their blood pressure back to an acceptable level.

I have blood pressure transducers which output amplified analog voltages. These voltages are digitized and recorded by a computer. BEFORE digitalization, I'd like to route my analog signal through an ON-OFF voltage-sensing switch with a threshold. Upon crossing the adjustable threshold, the switch would switch to ON, starting the pump.

For instance, my "good pressure" voltage would be 3V (DC); when the animal's pressure reaches a voltage of 2.5V (DC), the switch would turn on to start the pump to infuse the animal and get its pressure back up beyond 2.5V, at which point the pump would stop.

In my dreams, there would be three (3) thresholds to start three pumps. At 2.5V, Pump #1 starts. If that is not enough and the animal's pressure keeps dropping, Pump #2 is started when the voltage hits 2V. A third threshold (1.5V) would start a third pump. Together, these would work to infuse the animal with an increasing volume of fluid, maintaining its pressure high enough.

I can picture the system, but don't know how to build it. I have the pumps, the sensors, and the amplifiers. But I am missing the ON-OFF switching watchamacallit that will be configured with the threshold to activate the pumps.

All ideas are welcome! As mentioned, I am not an electronics expert, just a cardiologist. I appreciate your help.

Dan
 

Yaakov

Joined Jan 27, 2019
3,569
This is a good application for a microcontroller. Many people here have particular favorites and I expect you will get help on it. In any case, if you use an MCU you will have effectively unlimited flexibility, and with the current offerings and programming environments, it is easier than you might think.

I will leave it for the usual suspects to suggest particular hardware since they can provide more help executing the project.
 

sghioto

Joined Dec 31, 2017
2,395
But I am missing the ON-OFF switching watchamacallit that will be configured with the threshold to activate the pumps.
This module maybe all you would need depending on the pumps and sensors. This is a four channel relay board that is activated by comparing the input voltage from your sensor to an adjustable reference voltage on the module. It can be setup to activate the relays when the sensor voltage drops below the reference voltage. Channel #1 would be set for 2.5 volts, #2 for 2 volts and #3 for 1.5 volts.1614633438153.png

KNACRO 4-Channel 5V Voltage Comparator Module LM393 Voltage Comparator IC
 

Thread Starter

dsalvail

Joined Mar 1, 2021
3
Thanks Yaakov, and Sghioto. I don't have the schematics for the pumps; they work off 12V power supplies. The amplified pressure signal is DC volts, and I can make it as large or small as necessary.

The 4-Channel 5V Voltage Comparator Module LM393 Voltage Comparator IC looks really exciting! I notice it has a power jack: Does it mean it could potentially power my pumps director, as opposed to just acting as a pass-through for the current? In that case, it would be a relay, not a switch?

I've seen the 4-channel voltage comparator on Amazon; I'll give it a shot. Maybe it can power my pumps. If not, I'll use it as a switch, to allow through current from the pump's own power-supply.

I will let you know if this works!

Thanks again!

Dan
 

wayneh

Joined Sep 9, 2010
17,153
One concept you need to learn about and apply here is hysteresis, the gap between turning on and turning off. You don’t want a cliff that causes rapid toggling on and off. You want what your home thermostat does: the furnace comes on at one temp and turns off at one or two degrees higher. Then the furnace stays off then until the temperature falls below the lower threshold once again.
 

sghioto

Joined Dec 31, 2017
2,395
I notice it has a power jack: Does it mean it could potentially power my pumps director, as opposed to just acting as a pass-through for the current? In that case, it would be a relay, not a switch?
You would have to supply power to the module using a separate 5 volt supply.
The pumps would run off their own 12 volt supply through the relay contacts.
Wayneh is correct there may not be enough or any hysteresis on this module that may be a concern.
 

crutschow

Joined Mar 14, 2008
27,902
I notice it has a power jack
That's for applying power to the module.
You will need a small DC power supply of the appropriate voltage to power it.
You could use the pump power if you get a module that runs on the same voltage.
Otherwise a wallwort type supply should work fine for that.
 

Thread Starter

dsalvail

Joined Mar 1, 2021
3
I was concerned with the hysteresis, although I did not know this was the correct name for in in engineering. I assumed there was some of it built into the module, you know, a standard +/- 15% sort of thing. I'll see. I certainly cannot build any into the rest of the circuit; the pumps will be pre-programmed to deliver ON_OFF at a set rate, and the addition of Pump 1+Pump 2 +Pump 3 will provide 3 steps in infusion that will be reactive to the wellness of the animal.

I think I'll wait for Amazon to deliver the module and see how it connects up. I've found a 5/12/24V module, and the pumps run on 12V, so maybe the module can power them. If not, they all have power supplies. Whatever's simplest.

The project goes as follows: I induce septic shock into lab rats, and they develop it over 12 hours. I then need to monitor the intravenous infusion they require to stay alive, over the next 12 hours. That's the kicker: One way or another, in the absence of a reactive infusion system which can adapt to the animal's blood pressure, I need to sit in front of them for 12 hours straight and adjust the pumps manually. Of course, as soon as that experiment is done, I need to run to the hospital and let the other doctors at the ER know about the results: the human treatment gets adjusted immediately in clinical cases of sepsis and septic shock.

So on behalf of 300 000 Americans who dies every year of sepsis, thanks!

Dan
 

sghioto

Joined Dec 31, 2017
2,395
I've found a 5/12/24V module, and the pumps run on 12V, so maybe the module can power them. If not, they all have power supplies. Whatever's simplest.
Sort of the other way around. If you get a 12 volt module then you can power the module from the 12 volt pump supply. That would be the simplest method.
 

wayneh

Joined Sep 9, 2010
17,153
I was concerned with the hysteresis, although I did not know this was the correct name for in in engineering. I assumed there was some of it built into the module, you know, a standard +/- 15% sort of thing. I'll see.
I'd be surprised if it doesn't, since everyone that ever uses it will have the same issue. The only question is how big, and whether you can adjust it.
 
Top