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 | 3-digit frequencymeter

3-digit frequencymeter for SwissFlow flowsensor

This schematic is ment to digitally display the output of my electronic Swissflow SF800 flow sensor. This sensor puts out an open collector square wave signal (like a fan RPM monitoring signal) between 50Hz (=0.5 liter/minute) and 2000Hz (=20 liter/minute). By dividing the measured frequency by 10 and putting the decimal point at the right place you get directly a display in liter/minute. I don't use the first digit output (output D) from the 74C925 to obtain a display of 10 to 9990Hz or xx.x liter/minute. Resistor R1 (2k2) is there for accomodating the open collector output of the SF800 to a 5V TTL signal, available at connector J1.

The schematic I designed is based on a old well known Fairchild Semiconductor counter IC, the MM74C925. It's basically a 4-digit counter with seven segment-decoder & multiplexer and counter & latch registers.

The other sections of the schematic include a precise 0.5Hz timebase for the measuring time (during the positive cycle of the clock = 1 second = 1measure/2 seconds), based on a Philips HEF4521 crystal oscillator & 24-stage divider. This oscillator oscillates at 4.194308MHz and the output signal is taken from output Q23 which represents a dividing factor of 2^23 (=8.388.608) and serves as gate signal for IC3B (CD4093 NAND Schmitt trigger). Integrator IC3A creates the periodical latch enable signal and integrator IC3C produces the periodical reset signal, also from the 0.5Hz timebase signal.

The 7805 regulator delivers a stable 5V power supply from the 12V PSU line for the 74C925, the HEF4521 and the CD4093.

The segment driver output of the 74C925 is buffered by an ULN2003. With the shown values of R6-R12 (150 ohm) the peak output current per segment through the displays is about 40mA to compensate for the duty cycle of 25% and the multiplexing frequency of 1000Hz.

The 7-segment displays are (ofcourse) blue displays, the 0.56" common anode LT-5501 from Liteon. Blue leds have a forward voltage of about 3.8-4.0V, and taken into account the 0.9V saturation voltage of the ULN2003 output and the 0.7V saturation voltage of a BC327, +5V power supply was insufficient, and the displays are powered from the the +12V line. Since the digit driver outputs of the 74C925 only outputs 3 to 4 volts, it's not sufficient to saturate driver transistors T2, T4 and T6 (BC327 PNP's) and I added T1, T3, T5 (BC547 NPN's) to bypass this issue.

My Eheim 1250 pump delivers a flow of 1200 liter/minute at 0" head. Taken into account the pressure drop from radiator, water blocks, tubing and flow sensor it's quite possible that the final water flow will be under 10 liter/minute (600 liter/minute). In that case the first digit will always indicate "0". Therefore I will show both the schematics and PCB layouts for XX.X liter/minute display and for X.XX liter/minute display.

Flowmeter schematic for XX.X display

Flowmeter schematic for X.XX display

Flowmeter PCB layout for XX.X display	Flowmeter Display PCB layout for XX.X display
Download PCB layout in Circad'98 format	Download PCB layout in Circad'98 format

Flowmeter - Solder side

Flowmeter - Component side

Flowmeter Display - Solder side

Flowmeter Display - Component side

Mounted PCB's

Front view - In action

The two PCB's are soldered together by means of the solder pads at the edge of the main PCB, and the pads in the middle of the display PCB.

Fed with a square wave of 1280Hz

Idem - square wave 2630Hz

Mounted in a Lian Li bezel with blue plexi windows and together with my CPU speed indicator...

Mounted in the front panel of my PC-70...

General views of the front panel...

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