Lead Fault Indicator

[czmark]

Hey guys im trying to build a lead fault indicator by sending a small amount of current (bellow .01uA)
and once the continuity is broken the signal is saturated and a window comparator picks this up and sets off an alarm. Ill be using a pull up and pull down resistor to put the current into the patient or patient simulator.

just wondering if anyone has any experience building this and or have any tips for me.

thanks

 

[crutschow]

Is this an AC or DC signal?

 

[czmark]

its for a ECG so the QRS waveform. so once a lead comes off an alarm is set off.

 

[KeepItSimpleStupid]

You may want to take a look at these devices from Analog Devices: https://www.analog.com/en/analog-to-digital-converters/ad-converters/adas1000/products/product.html

 

[czmark]

i want to saturate the voltage negatively. so when a lead comes undone some how the pull down resistor will saturate it negativly so that my comparator will pick it up.

currently have the comparator set so if my signal drops bellow -2.5V the LED lights up as a warning.

anybody know how i can do this ?

 

[czmark]

okay guys ! got this thing to work. used pull down resistor and a negative voltage detector and it works.

only thing is that the voltage only saturates for like 2 seconds (-5 volts) then flat lines. then once the lead is placed on again a positive saturation goes on for like 5 seconds (+5 volts).

just wondering how i can do with this with an alarm. i was thinking a 555 timer set on monostable mode for about 30 seconds then when the lead is placed back on the positive saturation resets the 555 timer till the lead comes undone again?

anybody thinks this can work or have a better idea with a relay or something?

thanks!

 

[KeepItSimpleStupid]

Can you square it up to an edge with a schmidt trigger and then trigger a monostable (the CMOS one). Then use the resulting two signals to set and rest a flip flop.

Now you have a continuous signal or you can use the edge to trigger a 555 to get the longer delays or you can use one of the long timer CMOS chips.