This stress level Detector Circuit can be used as a Bio feedback control circuit for knowing the emotional status of a human brain and whether the person is suffering from a stressful condition or not.
The rising knowledge of the contributory role which stress performs in triggering health issues has contributed to enhanced desire for different kinds of 'autogenic' training as a technique of endorsing relaxation.
For example, several types of ' bio-feedback' circuits have grown to be famous, the theory is that particular physiological capabilities (heartbeat, body temperature, brain activity) is usually supervised and delivered within conscious effects of this issue.
How the Circuit Works
The stress or anxiety detector circuit explained in this article functions on the basic principle of supervising skin resistance as a measure of how stressed this issue is actually.
Precisely the same technique is employed in so-called lie detectors, yet, in that situation it is the qualified interpretation of the subject's reactions to a number of both innocuous and indicated queries which is essential.
The explanation of the circuit is as follows: variations in skin resistance (between electrodes E1 and E2) differ the frequency of the oscillator built round a 555 timer (1C10).
The output of the oscillator is fed to a 7490 divider (ICS), which in turn regulates the reset inputs of the counter produced by IC6 and IC7.
The result is that the period between successive pulses from IC10 establishes the number of clock pulses provided to this counter from a second oscillator (IC9).
The counter outputs are decoded and viewed on a pair of 7-segment displays, therefore offering a numerical sign of the subject ' s relative tenseness.
The frequency of the second oscillator, which is also formed by a 555 timer, is determined by C3 and R15.
By incorporating the circuit demonstrated in figure 2, several unique clock rates can be selected, thus permitting the sensitivity of the circuit to be varied to suit numerous situations.
In the beginning P1 ought to be modified to a suitably ' neutral ' position.
A pair of metal rings, which are slipped onto different fingers of the subject, will certainly demonstrate appropriate bio feedback detector sensors.
The rings could be linked to points E1 and E2 by proper lengths of wire.
The current utilization of the stress detector circuit is approximately 400 mA max.
To get rid of any kind of risk of electric shock, a proper care needs to be taken to make certain that the supply voltage is quite protected, preferably a battery should really be made use of.
Stress and Skin Temperature Meter Circuit
In this stress and skin temperature meter circuit a couple of analogue meters M1 and M2 individually keep track of skin resistance and skin temperature.
The skin resistance value could generate a varying pitch tone. Even though electronic stress meters are available, I and also analogue displays create modifications simpler to comply with.
The layout aims incorporated the necessity to produce a secure device without any in excess of about a volt placed on the skin.
I additionally needed an affordable battery life utilizing a single battery. The circuit (figure 1) provides four important stages: power supply, skin temperature meter, skin resistance meter and also the sound circuit.
Whenever SW1 is switched on, the 9V battery provides the audio circuit through volume regulate switch SW5. Diode D1 safeguards towards unintentional battery change.
IC3 and DR1 supply controlled +5V and +1.2V for the functional amplifiers. Battery output, potted down through R18 and R19, is in comparison with the stabilised 5V level.
If battery volts are low, comparator IC2a switches on a flashing LED. The skin resistance and temperature circuits employ identical inverting operational amplifier layouts.
The 1.2V supply is required as the virtual earth of the amplifiers. Therefore through the viewpoint of IC1a and IC1b, the probes are at a potential of -1.2V This "negative" voltage through the probes is inverted, amplified and provided to meters M1 and M2.
Different offset voltages or currents could be placed on back off the meter reading. Temperature of the skin could be calculated instantly (20 to 40 degrees C) once the Actual Temperature button SW2 is placed down.
Or else the meter M2 exhibits the temperature change from a mid scale initial setting. This mode features a sensitivity of +/- 1 degree C. Trimpot VT3 is utilized to build the genuine temperature range while the Temperature offset control RV3 sets the needle at the center within the sensitive range.
The temperature probe is certainly a temperature sensitive resistor constructed from semiconductor material. However the change of resistance in response to temperature is fairly non linear. R10 and R11 present linearisation as reviewed in a earlier post.
Having a sensitivity of 1 degree, self heating of the temperature sensor needs to be considered. R10 and R11 assist to reduce this impact by minimizing the amount of the 1.2V reference voltage which seems over the thermistor.
The skin resistance circuit employs performing pads linked to two fingers. A optimum of 1.2V is used across the pads and IC1a increases the resulting skin current.
Meter M1 measures the amplifier output. SW4 switches between the two skin resistance modes ESR and GSR. ESR (Electrical Skin Resistance) mode displays actual skin resistance once the ESR Basal button SW3 is pushed. Or else it exhibits resistance changes in accordance with an initial mid scale setting modified through RV2. GSR (Galvanic Skin Response) furthermore displays relative resistance changes however the gain could be converted to provide higher sensitivity.
In GSR mode, RV2 works like a gain control while offset is supplied by RV1. Remember that the Basal reading is worthless in GSR mode.
The sound circuit possesses a DC to frequency converter depending on the 555 timer IC4. Q2, R22 and C5 form an integrator by which C5 charges at a rate based on the output of 101a.
Once the upper voltage limit of the 555 is achieved. Q1 is switched on to release C5 once again. The pulse output through the timer is provided to a loudspeaker or earphone through sound amplifier 105.
Volume control RV4 as well includes SW5 such that the audio portion could be turned off individually.
Caution! For security factors this stress and skin temperature meter circuit equipment should not be modified for ac power or linked to mains electricity by any means.
