Hi guys, I am working on a project that ensures that the same current from a peripheral nerve stimulator e.g 0.5mA goes through each of the 5 resistances of a programmable potentiometer - this being confirmed by the LCD display. However, to do this I must connect an Arduino. I have racked my brain again and again and can't seem to get it right. For starters, the anode of the Nerve stimulator has to be connected to the ECG (during the actual operation of this device in Anaesthesia) whilst the cathode is the needle - which actually delivers current into the body! . But for the purpose of the experiments/project, I will not be using human tissue. Right now I am at a loss on how to make the connections of these terminals on Arduino UNO.
I have 30 years experience in electronics and am an Air Force trained hospital ICU tech and I don't have a clue either. Why ? Because I don't know what the device you are talking about is or what it's specifications are. Do you have a datasheet ? Telling us it has an anode and cathode and a current rating of 500uA is good start, but I don't know what kind of device it is. An led has and anode and a cathode. I rectifier diode has an anode and cathode.
I googled peripheral nerve stimulator and got this: http://bellmedical.com/ministim-peripheral-nerve-stimulator
If I just forget about you gizmo and say you have a device that draws 0.5mA (0.0005A) and you want to control the current with
a digital pot
each of the 5 resistances of a programmable potentiometer
I am working with a peripheral nerve stimulator. There are lots of them out there, but for my project, it is the Stimuplex HNS12 nerve stimulator by Braun which I am using as a model. Most anaesthetics find the combination of 0.3 - 0.5mA applied for 0.3 sec is sufficient to elicit a twitch in the muscle. I must make sure that the current delivered to the body tissue via the needle (cathode) is the same for widely varying overall resistances of the Nerve stimulator circuit - the variable aspect stemming mainly from the fact that different human beings have different skin/tissue impedances.
Note: all modern nerve stimulators are constant current generators (in order for them to cater for the widely varying resistances). They produce square waveforms of current too. Maximum operational current is 5mA.
Stimulating needle must be attached to the Cathode in order to reduce the amount of current required for stimulation of the nerve, since the outside of the cell membrane is more positive than the inside therefore it is a lot easier to depolarise the nerve cell membrane with cathodal current. On the other hand if needle is connected to the anode, hyperpolarisation would occur which would in turn prevent creation of an action potential(by depolarization) thereby leading to failure of a nerve block. So to increase the chances of a nerve block, the amount of current delivered to the tissues is key.
I have to test 3 - 5 resistors on a digital POT to ensure each of these resistors has the same amount of current flowing through e.g 0.5mA. This amount then has to be displayed on an LCD display.
The datasheet doesn't give the voltage. You will have to obtain a scope and measure the pwm frequency and voltage on the scope.
With R= UNKNOWN
and E= UNKNOWN,
I cannot tell you what resistances to use .
Get that information and we can go from there.
INSUFFICIENT DATA.
FYI,
The datasheet says max current is 5.00mA, not 0.5mA.