Cytron Technical Forum

hi there.. i tried to develop a device known as transcutenous electrical nerve stimulator. this device generate electrical current in digital signal pulsed and sent to skin surface using electrodes to kill pain. the original circuit of the device does not have any display, anyone of you know how to attach display into it? since this is analog device, so it is difficult to implement it. really needs help from expertise in analog circuit.. please

raichen WROTE:hi there.. i tried to develop a device known as transcutenous electrical nerve stimulator. this device generate electrical current in digital signal pulsed and sent to skin surface using electrodes to kill pain. the original circuit of the device does not have any display, anyone of you know how to attach display into it? since this is analog device, so it is difficult to implement it. really needs help from expertise in analog circuit.. please

Was it used in acupuncture where the electrodes are attached to the needles or was it like the OMRON muscle relaxation device?

In the first case, the impulse can be measured. Has to be filtered first to convert to square pulses then fed into the mcu to count the pulses/second=Frequency. The amplitude can also be measured analogously by the analog input of PIC. I have seen the inside of this type of circuit and it was just using 555 timer/oscillator with step-up multi-tapping transformers.

Allen

Have you checked the safety of this circuit?

Putting high currents through the body is dangerous. If this is the FYP - discuss with your supervisor about the safety of the equipment before putting this on the human body.

this unit use electrode attached to the skin surface only.. and use only supplies from battery, probably 9V and step up to about 80V. the voltage can be change according to user's need. and the max will be as i said about 80v. this is what i get from the article i read.

ABSF,

could you please explain more about the impulse that can be measures.. im not completely understand actually.. thank you..

The above is just a block diagram to demonstrate my idea. If there is no such points where the signals are available, try to make them available. I hope you're not buying a commercial product and try to modify it as I know factory made test equipments have ways to protect their designs so others cant copy them.

Allen

ABSF,

did you mean output from the oscillating switches uses as input to the MCU unit? and that for displaying the frequency selection? And then output from the step up circuit uses as analog input to measure amplitude of pulses? both of this then being displayed? is that right?

how about the voltage that is varied using variable resistor.. the voltage would be around 9 -80v like that? my intention is to display the voltage selection, freq and also pulse width.

raichen WROTE:did you mean output from the oscillating switches uses as input to the MCU unit? and that for displaying the frequency selection? And then output from the step up circuit uses as analog input to measure amplitude of pulses? both of this then being displayed? is that right?

I dont understand what you meant by "oscillating switches" and "frequency selection"? Can you explain in simple sentences?

Yes both the frequency and pulse amplitude can be displayed on the LCD.

raichen WROTE:how about the voltage that is varied using variable resistor.. the voltage would be around 9 -80v like that? my intention is to display the voltage selection, freq and also pulse width.

That semi-variable resistor is used as a voltage divider for the ADC input. The PIC can only tolerate 5V input, so the 80V has to be scaled down by a factor of 16 so that 0-80V will appear as between 0-5V on the PIC. Inside the PIC, the 0-5V is converted to a "number" between 0-1023 by ADC (10 bit resolution). So 1023 will be corresponding to 80V. The amplitude can be calculated by dividing the "number" by 12.8 to get the actual voltage from your circuit. Which means every 12.8 counts is equivalent to 1 volt of the amplitude measured.

Your voltage selection has nothing to do with the mcu. The mcu only measures what is outputted from your circuit. As for the pulse width measurement, I have not yet come out with a solution. May be other members here can help.

I am not sure if the ADC can take AC waveform. If it cant, the 80V pulses has to be rectified before entering the voltage divider. A 5.1V zener is recommended to be placed at the input of the PIC to prevent any high voltage burning off the PIC.

BTW I am just curious whether you an engineering student or a medical student?

Allen

ABSF,

thanks you for your explanations. It do help me a lot to understand of what you meant.