Free Electronic Circuit | Oxygen Sensor Simulator

Oxygen Sensor Simulator The oxygen sensor simulator as built on a protoboard. Note the cigarette lighter plug used for power source. The adjustment knob is at the left, and the switch is on the right. The red indicator LED is in the middle. Only use red, because the voltage drop of the LED is part of the circuit! The schematic diagram for the simulator. Closing the switch engages the simulator. Turning the knob clockwise simulates a lean condition, turns the LED off, and the car should start running rich to compensate. The big "V" is a digital voltmeter(not shown in the pictures). Using a smaller value for C1, perhaps 4.7 uF, will make the circuit oscillate faster and might be more like a real oxygen sensor(a new sensor switches more often than an old one). The adapter cable. Note the connector recycled from an old oxygen sensor. Hard to see under the black tape: 100K resistor. The schematic diagram of the adapter cable and oxygen sensor. Note the heater is shown as a resistor, mine measured about 7 ohms. Previous page... Frequently Asked Questions:

Q: Will you build one of these for me, or sell me the one you built? A: No, I won’t do that. If there is a community college or high school near you with an electronics class, you should contact the instructor and ask if there are students looking for a small job. This project is simple enough it should not pose a problem. Q: I built the project but I have to fiddle with the knob all the time. A: The car eventually will get too rich or too lean because it isn’t using the oxygen sensor anymore. This is a diagnostic aid, not a long-term replacement for an oxygen sensor. Q: I do racing on the weekends with my street car. Will this project help me tune the car to different conditions? A: If you do drag racing, yes. The races are short enough you can set a mixture and it will hold long enough. Each time you start the car it will go to the mixture you set. Other forms of racing take too long, and the mixture will creep towards very rich, you’d have to adjust the knob while driving.

Free Electronic Circuit | Infra-red Level Detector

Useful for liquids level detection and proximity devices

Up to 50 cm. range, optional relay operation

Circuit diagram:

Parts:

R1_____________10K   1/4W Resistor R2,R5,R6,R9_____1K   1/4W Resistors R3_____________33R   1/4W Resistor R4,R8___________1M   1/4W Resistors R7_____________10K   Trimmer Cermet R10____________22K   1/4W Resistor   C1,C4___________1µF  63V Electrolytic or Polyester Capacitors C2_____________47pF  63V Ceramic Capacitor C3,C5,C6______100µF  25V Electrolytic Capacitors  D1_____________Infra-red LED D2_____________Infra-red Photo Diode (see Notes) D3,D4________1N4148  75V 150mA Diode D5______________LED  (Any color and size) D6,D7________1N4002  100V 1A Diodes  Q1____________BC327  45V 800mA PNP Transistor  IC1_____________555  Timer IC IC2___________LM358  Low Power Dual Op-amp IC3____________7812  12V 1A Positive voltage regulator IC  RL1____________Relay with SPDT 2A @ 220V switch                Coil Voltage 12V. Coil resistance 200-300 Ohm  J1_____________Two ways output socket 

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Device purpose:

This circuit is useful in liquids level or proximity detection. It operates detecting the distance from the target by reflection of an infra-red beam. It can safely detect the level of a liquid in a tank without any contact with the liquid itself. The device's range can be set from a couple of cm. to about 50 cm. by means of a trimmer.
Range can vary, depending on infra-red transmitting and receiving LEDs used and is mostly affected by the color of the reflecting surface. Black surfaces lower greatly the device's sensitivity.

Circuit operation:

IC1 forms an oscillator driving the infra-red LED by means of 0.8mSec. pulses at 120Hz frequency and about 300mA peak current. D1 & D2 are placed facing the target on the same line, a couple of centimeters apart, on a short breadboard strip. D2 picks-up the infra-red beam generated by D1 and reflected by the surface placed in front of it. The signal is amplified by IC2A and peak detected by D4 & C4. Diode D3, with R5 & R6, compensates for the forward diode drop of D4. A DC voltage proportional to the distance of the reflecting object and D1 & D2 feeds the inverting input of the voltage comparator IC2B. This comparator switches on and off the LED and the optional relay via Q1, comparing its input voltage to the reference voltage at its non-inverting input set by the Trimmer R7.

Notes:

• Power supply must be regulated (hence the use of IC3) for precise reference voltage. The circuit can be fed by a commercial wall plug-in adapter, having a DC output voltage in the range 12-24V.
• Current drawing: LED off 40mA; LED and Relay on 70mA @ 12V DC supply.
• R10, C6, Q1, D6, D7, RL1 and J1 can be omitted if relay operation is not required.
• The infra-red Photo Diode D2, should be of the type incorporating an optical sunlight filter: these components appear in black plastic cases. Some of them resemble TO92 transistors: in this case, please note that the sensitive surface is the curved, not the flat one.
• Avoid sun or artificial light hitting directly D1 & D2.
• Usually D1-D2 optimum distance lies in the range 1.5-3 cm.
• If you are needing a similar circuit driving 3 LEDs in sequence, also suitable as a parking aid

Free Electronic Circuit | Car Parking Sensor

Three LEDs signal bumper-barrier distance

Infra-red operation, indoor use

Circuit diagram:

Parts:

R1_____________10K   1/4W Resistor R2,R5,R6,R9_____1K   1/4W Resistors R3_____________33R   1/4W Resistor R4,R11__________1M   1/4W Resistors R7______________4K7  1/4W Resistor R8______________1K5  1/4W Resistor R10,R12-R14_____1K   1/4W Resistors   C1,C4___________1µF  63V Electrolytic or Polyester Capacitors C2_____________47pF  63V Ceramic Capacitor C3,C5_________100µF  25V Electrolytic Capacitors  D1_____________Infra-red LED D2_____________Infra-red Photo Diode (see Notes) D3,D4________1N4148  75V 150mA Diodes D5-7___________LEDs  (Any color and size)  IC1_____________555  Timer IC IC2___________LM324  Low Power Quad Op-amp IC3____________7812  12V 1A Positive voltage regulator IC 

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Device purpose:

This circuit was designed as an aid in parking the car near the garage wall when backing up. LED D7 illuminates when bumper-wall distance is about 20 cm., D7+D6 illuminate at about 10 cm. and D7+D6+D5 at about 6 cm. In this manner you are alerted when approaching too close to the wall.
All distances mentioned before can vary, depending on infra-red transmitting and receiving LEDs used and are mostly affected by the color of the reflecting surface. Black surfaces lower greatly the device sensitivity.
Obviously, you can use this circuit in other applications like liquids level detection, proximity devices etc.

Circuit operation:

IC1 forms an oscillator driving the infra-red LED by means of 0.8mSec. pulses at 120Hz frequency and about 300mA peak current. D1 & D2 are placed facing the car on the same line, a couple of centimeters apart, on a short breadboard strip fastened to the wall. D2 picks-up the infra-red beam generated by D1 and reflected by the surface placed in front of it. The signal is amplified by IC2A and peak detected by D4 & C4. Diode D3, with R5 & R6, compensates for the forward diode drop of D4. A DC voltage proportional to the distance of the reflecting object and D1 & D2 feeds the inverting inputs of three voltage comparators. These comparators switch on and off the LEDs, referring to voltages at their non-inverting inputs set by the voltage divider resistor chain R7-R10.

Circuit modification:

A circuit modification featuring an audible alert instead of the visual one is available here:Park-Aid Modification

Notes:

• Power supply must be regulated (hence the use of IC3) for precise reference voltages. The circuit can be fed by a commercial wall plug-in adapter, having a DC output voltage in the range 12-24V.
• Current drawing: LEDs off 40mA; all LEDs on 60mA @ 12V DC supply.
• The infra-red Photo Diode D2, should be of the type incorporating an optical sunlight filter: these components appear in black plastic cases. Some of them resemble TO92 transistors: in this case, please note that the sensitive surface is the curved, not the flat one.
• Avoid sun or artificial light hitting directly D1 & D2.
• If your car has black bumpers, you can line-up the infra-red diodes with the (mostly white) license or number plate.
• It is wiser to place all the circuitry near the infra-red LEDs in a small box. The 3 signaling LEDs can be placed far from the main box at an height making them well visible by the car driver.
• The best setup is obtained bringing D2 nearer to D1 (without a reflecting object) until D5 illuminates; then moving it a bit until D5 is clearly off. Usually D1-D2 optimum distance lies in the range 1.5-3 cm.
• If you are needing a simpler circuit of this kind driving a LED or a relay, click Infra-red Level Detector

Engineering Projects | Ultrasonic Parking Sonar

Ultrasonic Parking Sonar

This circuit electronic is an ultrasonic parking sonar. Based on an ultrasonic amplifier from an article seen on a 1982 magazine, it was once installed on the rear bumper of my Volvo Station Wagon. It served very well for many years. Connecting it to the reverse gear lights, it switches on automatically and shows you the distance to the nearest obstacle (according to his beam) on a led scale. When the last led lights, a buzzer is also activated telling you to stop

Feautures:

• automatic switch on on rear gear


• led-bargraph display


• audible bleep on last led


• "good old" design style, no microcontrollers!
  
  

It works on the sonar principle, sending an ultrasound burst and listening for first echo. The burst generated by the oscillator built around U4D (you must set the frequency using TR2 to have 40 kHz or the maximum sensitivity), U4E buffers the output and U4F boost the signal doubling the voltage span across the TX piezo transducer .

Free electronic circuit | Almost Ultrasonic Motion Sensor

Almost Ultrasonic Motion Sensor | Security System

This sensor uses the sound generator in the RCX to make a 15kHz audio tone, which is almost ultrasonic. The tone is received with circuitry similar to my Sound sensor. The output of a crystal microphone MIC is amplified and then only the very high frequencies are further amplified (see plot). This signal is enveloped detected with a diode D1 and capacitor C1. The voltage on the capacitor will equal the average volume of high frequency sound the microphone is picking up at any moment. Motion of objects near to the RCX and microphone cause the volume level to vary as the signal path and distance between them changes. The variation in level is further amplified and fed to the RCX. The RCX sees a level of about 31 when there is no motion, and peaks to over 50 when there is rapid significant motion.

The circuit diagram is below. An LM324 quad Opamp is used for all stages, and the diodes are all 1N4148s.

This is a plot of the frequency response of the High Frequency Amplifier stage. The gain has been set to peak at about 15kHz so that interference from other sounds is minimized.

Here is a photo of my finished sensor. I built it on a piece of PC board and mounted it inside of a LEGO #5391 9V Battery Box. The microphone is attached to the end with double face foam tape.

Here is how I tested the circuit. The RCX has a Visual Basic program that produces a 15kHz tone and watches the input for levels over 33. If is sees one, it turns on an output which just has a light hooked up to it. The operating range depends on many mechanical factors. It can pickup motion of large objects 8" away while small objects may need to be only a few inches between the RCX and the microphone.

Here is the very simple VB code:

.BeginOfTask 0  .SetSensorType 1, 3  .SetPower "0", 2, 7  .Loop 2, 0   .PlayTone 15000, 25   .If 9, 1, 0, 2, 33    .On "0"   .Else    .Off "0"   .EndIf  .EndLoop  .EndOfTask

Free electronic circuit | Radio Wave Alarm

Radio Wave Alarm | Security System

This alarm circuit is sure to have the police beating a path to your door - however, it has the added advantage of alerting you to their presence even before their footsteps fall on the doormat.



The circuit transmits on Medium Wave (this is the small problem with the police). IC1a, together with a sensor (try a 20cm x 20cm sheet of tin foil) oscillates at just over 1MHz. This is modulated by an audio frequency (a continuous beep) produced by IC1b. When a hand or a foot approaches the sensor, the frequency of the transmitter (IC1a) drops appreciably.

Suppose now that the circuit transmits at 1MHz. Suppose also that your radio is tuned to a frequency just below this. The 1MHz transmission will therefore not be heard by the radio. But bring a hand or a foot near to the sensor, and the transmitter's frequency will drop, and a beep will be heard from the radio.



Attach the antenna to a multiplug adapter that is plugged into the mains, and you will find that the Medium Wave transmission radiates from every wire in your house. Now place a suitably tuned Medium Wave radio near some wires or a plug point in your house, and an early-warning system is set up.



Instead of using the sheet of tin foil as the sensor, you could use a doorknob, or burglar bars. Or you could use a pushbutton and seriesresistor (wired in series with the 33K resistor - the pushbutton would short it out) to decrease the frequency of IC1a, so activating the system by means of a pushbutton switch. In this case, the radio would be tuned to a frequency just below that of the transmitter.

Free Electronic Circuit | Water Activated Alarm

Water Activated Alarm | Security System

The Electronic circuit uses a 555 timer wired as an astable oscillator and powered by the emitter current of the BC109C. Under dry conditions, thetransistor will have no bias current and be fully off. As the probes get wet, a small current flows between base and emitter and the transistor switches on. A larger current flows in the collector electronic circuit enabling the 555 osillator to sound.

An On/Off switch is provided and remember to use a non-reactive metal for the probe contacts. Gold or silver plated contacts from an old relay may be used, however a cheap alternative is to wire alternate copper strips from a piece of veroboard. These will eventually oxidize over but as very little current is flowing in the base circuit, the higher impedance caused by oxidization is not important. No base resistor is necessary as the transistoris in emitter follower, current limit being the impedance at the emitter (the oscillator circuit).