Electronic Stethoscope

Stethoscopes are not only useful for doctors, but home mechanics, exterminators, spying and any number of other uses. Standard stethoscopes provide no amplification which limits their use. This circuit uses op-amps to greatly amplify a standard stethoscope, and includes a low pass filter to remove background noise.


Parts

Part Total Qty. Description

R1 ---------------1 ----------- 10K 1/4W Resistor
R2 ---------------1 ----------- 2.2K 1/4W Resistor
R4 ---------------1------------ 47K 1/4W Resistor
R5, R6, R7 -------3------------ 33K 1/4W Resistor
R8 ---------------1 ----------- 56K 1/4W Resistor
R10 --------------1 ----------- 4.7K 1/4W Resistor
R11 --------------1 ------------ 2.2K to 10K Audio Taper Pot
R12 --------------1------------ 330K 1/4W Resistor
R13, R15, R16---- 3------------ 1K 1/4W Resistor
R14 --------------1 ----------- 3.9 Ohm 1/4W Resistor
C1, C8 -----------2 ---------- 470uF 16V Electrolytic Capacitor
C2 ---------------1-----------4.7uF 16V Electrolytic Capacitor
C3, C4 -----------2----------- 0.047uF 50V Metalized Plastic Film Capacitor
C5 ---------------1----------- 0.1uF 50V Ceramic Disc Capacitor
C6, C7 -----------2----------- 1000uF 16V Electrolytic Capacitor
U1 ---------------1 ----------- TL072 Low Noise Dual Op-Amp
U4 ---------------1----------- 741 Op-Amp
U5 ---------------1----------- LM386 Audio Power Amp
MIC --------------1 -----------Two Wire Electret Microphone
J1 ----------------1 -----------1/8" Stereo Headphone Jack
Batt1, Batt2 ------2----------- 9V Alkaline Battery
LED --------------1 ----------- Red/Green Dual Colour Two Wire LED
SW ---------------1 ----------- DPST Switch
MISC -------------1 ----------- Stethoscope head or jar lid, rubber sleeve for microphone, board, wire, battery clips, knob for R11

Notes

• MIC is an assembly made out of a stethoscope head and electret mic. Cut the head off the stethoscope and use a small piece of rubber tube to join the nipple on the head to the mic.
• Be careful with the volume, as excess noise levels may damage your ears.
• R11 is the volume control.
• The circuit marked as optional is not required for the main circuit to function. The optional circuit blinks an LED to the heartbeat as it is heard by the microphone. Even if the optional circuit is not included, sound will still be heard via the headphone jack.

Muscular Bio-Stimulator

Particularly suitable for cellulite treatment
3V battery supply, portable set

Device purpose:

This is a small, portable set, designed for those aiming at look improvement. The Bio-Stimulator provides muscles' stimulation and invigoration but, mainly, it could be an aid in removing cellulite.


Tape the electrodes to the skin at both ends of the chosen muscle and rotate P1 knob slowly until a light itch sensation is perceived. Each session should last about 30 - 40 minutes.

Parts:

• P1______________4K7 Linear Potentiometer
• R1____________180K 1/4W Resistor
• R2______________1K8 1/4W Resistor (see Notes)
• R3______________2K2 1/4W Resistor
• R4____________100R 1/4W Resistor
• C1____________100nF 63V Polyester Capacitor
• C2____________100µF 25V Electrolytic Capacitor
• D1______________LED Red 5mm.
• D2___________1N4007 1000V 1A Diode
• Q1,Q2_________BC327 45V 800mA PNP Transistors
• IC1____________7555 or TS555CN CMos Timer IC
• T1_____________220V Primary, 12V Secondary 1.2VA Mains transformer (see Notes)
• SW1____________SPST Switch (Ganged with P1)
• B1_____________3V Battery (two 1.5V AA or AAA cells in series etc.)

Warning:

The use of this device is forbidden to Pace-Maker bearers and pregnant women.
Do not place the electrodes on cuts, wounds, injuries or varices.
Obviously we can't claim or prove any therapeutic effectiveness for this device.

Circuit operation:

IC1 generates 150µSec. pulses at about 80Hz frequency. Q1 acts as a buffer and Q2 inverts the polarity of the pulses and drives the Transformer. The amplitude of the output pulses is set by P1 and approximately displayed by the brightness of LED D1. D2 protects Q2 against high voltage peaks generated by T1 inductance during switching.

Notes:

• T1 is a small mains transformer 220 to 12V @ 100 or 150mA. It must be reverse connected i.e. the 12V secondary winding across Q2 Collector and negative ground, and the 220V primary winding to output electrodes.
• Output voltage is about 60V positive and 150V negative but output current is so small that there is no electric-shock danger.
• In any case P1 should be operated by the "patient", starting with the knob fully counter-clockwise, then rotating it slowly clockwise until the LED starts to illuminate. Stop rotating the knob when a light itch sensation is perceived.
• Best knob position is usually near the center of its range.
• In some cases a greater pulse duration can be more effective in cellulite treatment. Try changing R2 to 5K6 or 10K maximum: stronger pulses will be easily perceived and the LED will shine more brightly.
• Electrodes can be obtained by small metal plates connected to the output of the circuit via usual electric wire and can be taped to the skin. In some cases, moistening them with little water has proven useful.
• SW1 should be ganged to P1 to avoid abrupt voltage peaks on the "patient's" body at switch-on, but a stand alone SPST switch will work quite well, provided you remember to set P1 knob fully counter-clockwise at switch-on.
• Current drawing of this circuit is about 1mA @ 3V DC.
• Some commercial sets have four, six or eight output electrodes. To obtain this you can retain the part of the circuit comprising IC1, R1, R2, C1, C2, SW1 and B1. Other parts in the diagram (i.e. P1, R3, R4, D1, D2, Q2 & T1) can be doubled, trebled or quadrupled. Added potentiometers and R3 series resistors must be wired in parallel and all connected across Emitter of Q1 and positive supply.
• Commercial sets have frequently a built-in 30 minutes timer. For this purpose you can use the Timed Beeper the Bedside Lamp Timer or the Jogging Timer circuits available on this Website, adjusting the timing components to suit your needs.

Automatic Room Lights

n ordinary automatic room power control circuit has only one light sensor. So when a person enters the room it gets one pulse and the lights come ‘on.’ When the person goes out it gets another pulse and the lights go ‘off.’ But what happens when two persons enter the room, one after the other? It gets two pulses and the lights remain in ‘off’ state. The circuit described here overcomes the above-mentioned problem. It has a small memory which enables it to automatically switch ‘on’ and switch ‘off’ the lights in a desired fashion. The circuit uses two LDRs which are placed one after another (separated by a distance of say half a metre) so that they may separately sense a person going into the room or coming out of the room. Outputs of the two LDR sensors, after processing, are used in conjunction with a bicolour LED in such a fashion that when a person gets into the room it emits green light and when a person goes out of the room it emits red light, and vice versa.



These outputs are simultaneously applied to two counters. One of the counters will count as +1, +2, +3 etc when persons are getting into the room and the other will count as -1, -2, -3 etc when persons are getting out of the room. These counters make use of Johnson decade counter CD4017 ICs. The next stage comprises two logic ICs which can combine the outputs of the two counters and determine if there is any person still left in the room or not. Since in the circuit LDRs have been used, care should be taken to protect them from ambient light. If desired, one may use readily available IR sensor modules to replace the LDRs.

The sensors are installed in such a way that when a person enters or leaves the room, he intercepts the light falling on them sequentially—one after the other. When a person enters the room, first he would obstruct the light falling on LDR1, followed by that falling on LDR2. When a person leaves the room it will be the other way round. In the normal case light keeps falling on both the LDRs, and as such their resistance is low (about 5 kilo-ohms). As a result, pin 2 of both timers (IC1 and IC2), which have been configured as monostable flip-flops, are held near the supply voltage (+9V).

When the light falling on the LDRs is obstructed, their resistance becomes very high and pin 2 voltages drop to near ground potential, thereby triggering the flip-flops. Capacitors across pin 2 and ground have been added to avoid false triggering due to electrical noise. When a person enters the room, LDR1 is triggered first and it results in triggering of monostable IC1.

The short output pulse immediately charges up capacitor C5, forward biasing transistor pair T1-T2. But at this instant the collectors of transistors T1 and T2 are in high impedance state as IC2 pin 3 is at low potential and diode D4 is not conducting. But when the same person passes LDR2, IC2 monostable flip-flop is triggered. Its pin 3 goes high and this potential is coupled to transistor pair T1-T2 via diode D4. As a result transistor pair T1-T2 conducts because capacitor C5 retains the charge for some time as its discharge time is controlled by resistor R5 (and R7 to an extent).

Thus green LED portion of bi-colour LED is lit momentarily. The same output is also coupled to IC3 for which it acts as a clock. With entry of each person IC3 output (high state) keeps advancing. At this stage transistor pair T3-T4 cannot conduct because output pin 3 of IC1 is no longer positive as its output pulse duration is quite short and hence transistor collectors are in high impedance state. When persons leave the room, LDR2 is triggered first followed by LDR1.

Since the bottom half portion of circuit is identical to top half, this time with the departure of each person red portion of bi-colour LED is lit momentarily and output of IC4 advances in the same fashion as in case of IC3. The outputs of IC3 and those of IC4 (after inversion by inverter gates N1 through N4) are ANDed by AND gates (A1 through A4) are then wire ORed (using diodes D5 through D8). The net effect is that when persons are entering, the output of at least one of the AND gates is high, causing transistor T5 to conduct and energise relay RL1.

The bulb connected to the supply via N/O contact of relay RL1 also lights up. When persons are leaving the room, and till all the persons who entered the room have left, the wired OR output continues to remain high, i.e. the bulb continues to remains ‘on,’ until all persons who entered the room have left. The maximum number of persons that this circuit can handle is limited to four since on receipt of fifth clock pulse the counters are reset.

The capacity of the circuit can be easily extended for up to nine persons by removing the connection of pin 1 from reset pin (15) and utilising Q1 to Q9 outputs of CD4017 counters. Additional inverters, AND gates and diodes will, however, be required.

Running Message Display

Light emitting diodes are advan- tageous due to their smaller size, low current consumption and catchy colours they emit. Here is a running message display circuit wherein the letters formed by LED arrangement light up progressively. Once all the letters of the message have been lit up, the circuit gets reset. The circuit is built around Johnson decade counter CD4017BC (IC2). One of the IC CD4017BE’s features is its provision of ten fully decoded outputs, making the IC ideal for use in a whole range of sequencing operations. In the circuit only one of the outputs remains high and the other outputs switch to high state successively on the arrival of each clock pulse.



The timer NE555 (IC1) is wired as a 1Hz astable multivibrator which clocks the IC2 for sequencing operations. On reset, output pin 3 goes high and drives transistor T7 to ‘on’ state. The output of transistor T7 is connected to letter ‘W’ of the LED word array (all LEDs of letter array are connected in parallel) and thus letter ‘W’ is illuminated. On arrival of first clock pulse, pin 3 goes low and pin 2 goes high. Transistor T6 conducts and letter ‘E’ lights up. The preceding letter ‘W’ also remains lighted because of forward biasing of transistor T7 via diode D21. In a similar fashion, on the arrival of each successive pulse, the other letters of the display are also illuminated and finally the complete word becomes visible. On the following clock pulse, pin 6 goes to logic 1 and resets the circuit, and the sequence repeats itself. The frequency of sequencing operations is controlled with the help of potmeter VR1.

The display can be fixed on a veroboard of suitable size and connected to ground of a common supply (of 6V to 9V) while the anodes of LEDs are to be connected to emitters of transistors T1 through T7 as shown in the circuit. The above circuit is very versatile and can be wired with a large number of LEDs to make an LED fashion jewellery of any design. With two circuits connected in a similar fashion, multiplexing of LEDs can be done to give a moving display effect.

Electronic Scoring Game

You can play this game alone or with your friends. The circuit comprises a timer IC, two decade counters and a display driver along with a 7-segment display.

The game is simple. As stated above, it is a scoring game and the competitor who scores 100 points rapidly (in short steps) is the winner. For scoring, one has the option of pressing either switch S2 or S3. Switch S2, when pressed, makes the counter count in the forward direction, while switch S3 helps to count downwards. Before starting a fresh game, and for that matter even a fresh move, you must press switch S1 to reset the circuit. Thereafter, press any of the two switches, i.e. S2 or S3.

On pressing switch S2 or S3, the counter’s BCD outputs change very rapidly and when you release the switch, the last number remains latched at the output of IC2. The latched BCD number is input to BCD to 7-segment decoder/driver IC3 which drives a common-anode display DIS1. However, you can read this number only when you press switch S4. The sequence of operations for playing the game between, say two players ‘X’ and ‘Y’, is summarised below:

Player ‘X’ starts by momentary pressing of reset switch S1 followed by pressing and releasing of either switch S2 or S3. Thereafter he presses switch S4 to read the display (score) and notes down this number (say X1) manually.
Player ‘Y’ also starts by momentary pressing of switch S1 followed by pressing of switch S2 or S3 and then notes down his score (say Y1), after pressing switch S4, exactly in the same fashion as done by the first player.
Player ‘X’ again presses switch S1 and repeats the steps shown in step 1 above and notes down his new score (say, X2). He adds up this score to his previous score. The same procedure is repeated by player ‘Y’ in his turn.
The game carries on until the score attained by one of the two players totals up to or exceeds 100, to be declared as the winner.

Several players can participate in this game, with each getting a chance to score during his own turn. The assembly can be done using a multipurpose board. Fix the display (LEDs and 7-segment display) on top of the cabinet along with the three switches. The supply voltage for the circuit is 5V

3 Channel Spectrum Analyzer

This 3 channel 15 LED spectrum analyzer is the perfect addition to any audio amp project. It produces fantastic displays on three LED bars that can be individually adjusted for any particular frequency range. The circuit will take line level output from most any audio source, and operates on 12V DC. This means that it can even be run in a car.



Part

• R1 ------------------------ 1 100K 1/4W Resistor
• R2 ------------------------ 1 820K 1/4W Resistor
• R3, R14, R16, R18 ---------- 4 2.2 Meg 1/4W Resistor
• R4, R5, R6 ---------------- 3 22K Pot
• R7, R8, R9, R25, R27, R29 -- 6 10K 1/4W Resistor
• R10, R11, R12 -------------- 3 680 Ohm 1/4W Resistor
• R13. R15, R17 -------------- 3 580K 1/4W Resistor
• R19, R20, R21 -------------- 3 39K 1/4W Resistor
• R22, R23, R24 -------------- 3 47K 1/4W Resistor
• R26, R28, R30 -------------- 3 33 Ohm 1/4W Resistor
• C1, C5, C6 -------------- 3 0.012uF Polystyrene Capacitor
• C2, C9, C10, C11 ----------- 4 3.3uF Electrolytic Capacitor
• C3, C4 -------------------- 2 0.0022uF Polystyrene Capacitor
• C7, C8 -------------------- 2 47nF Polystyrene Capacitor
• C12, C13, C14 -------------- 3 0.47uF Electrolytic Capacitor
• C15, C16, C17 -------------- 3 22uF Electrolytic Capacitor
• D1, D2, D3 ----------------- 3 1N4002 Silicon Diode
• D4, D5, D6, D8, D8 --------- 5 Green LED
• D10, D11, D12, D13, D14 ---- 5 Amber LED
• D16, D17, D18, D19, D20 ---- 5 Red LED
• U1 ------------------------ 1 LM3900 Quad Op Amp
• U2, U3, U4 ----------------- 3 AN6884 Bar Graph IC
• MISC -------------------- 1 Board, Wires, Sockets For ICs

Notes:

• The circuit expects line level inputs. If you connect it to speaker level, you will have to readjust the circuit every time you change the volume.
• After the circuit is connected, apply power and signal. Now adjust the pots until the corresponding group of LEDs reacts.