Voltmeters

This screen uses ten LEDs to display a voltage range of 10.5 to 15 volts. Each LED represents a step 0.5wvolt tension. The heart of the circuit is the 3914 points LM / bar display driver. Trimming potentiometer R5 is adjusted so that 7.5 volts is applied to the upper side of the bulkhead. D2 resistor R7 and diode D5 to tighten the voltage applied to the LED 3 volts. A lowpass filter consisting of L1 and C2 guards against voltage spikes. The diode D1 is used to protect against reverse voltage where the voltmeter is connected backwards. ..

Humidity Sensor with the H14DL

Humidity Sensor with the H14DL

A humidity sensor with temperature compensation built-in. Never apply a DC voltage to the sensor, even measuring the sensor with an ohmmeter will damage the device, always ensure that an AC voltage is applied. Avoid condensation, freezing, dust, mist, oil, alcohol, etc. To set up this circuit replace the H14DL with Min Res 22Kohm and Min Res 51Kohm as shown, Acjust RV1 until a voltmeter between output and ground reads 1.40V. ..

Analog Volt and ampere meter

Analog Volt and ampere meter

For those who labvoeding built and flow of tension and a leader in providing circuit below was developed. If meter is a moving-coil meter 100?A useful. You have to make yourself a new scale. Also useful is a moving coil meter Conrad sells. This meter has already graduated to 30V and 1.5 A. S1 can be omgechakeld between volts and current measurement...

Automotive voltage tester schematic

Automotive voltage tester schematic

This is a simple spanniningszoeker that is very suitable for car, for connection of alarm systems, handsfree kits, radios, etc. At rest, the yellow LED because the path of least resistance. If the probe with a positive or negative pole connected is coming and the red or green and yellow LED light goes out. The yellow LED also serves as a check or put pressure on the circuit state...

99 mV to 999 mV meter schematic

99 mV to 999 mV meter schematic

This circuit can for example be incorporated into a diet to pressure warning. The meter can measure voltages from -99 mV to 999 mV. The circuit uses two ICs, the CA 3161 and CA 3162. IC1 converts the analog signal into a digital signal. IC1 is also the multiplexed signal to T1-T3 can be controlled. The BCD code is then fed to IC1 IC2, a BCD/7-segments converter. Then the signal is fed to the displays. Pin 6 of IC1 (hold) can be used for a number of things. When pin 6 is grounded or open, the 4 Hz sampling frequency. When pin 6 is at 1.2 V, then enter the HOLD function is activated. ..

12V Battery Meter with 4 LEDs

12V Battery Meter with 4 LEDs

In the circuit below, a quad voltage comparator (LM339) is used as a simple bar graph meter to indicate the charge condition of a 12 volt, lead acid battery. A 5 volt reference voltage is connected to each of the (+) inputs of the four comparators and the (-) inputs are connected to successive points along a voltage divider. The LEDs will illuminate when the voltage at the negative (-) input exceeds the reference voltage. Calibration can be done by adjusting the 2K potentiometer so that all four LEDs illuminate when the battery voltage is 12.7 volts, indicating full charge with no load on the battery. ..

Milliamp Meter to Voltmeter

Milliamp Meter to Voltmeter

A milliamp meter can be used as a volt meter by adding a series resistance. The resistance needed is the full scale voltage reading divided by the full scale current of the meter movement. So, if you have a 1 milliamp meter and you want to read 0-10 volts you will need a total resistance of 10/.001 = 10K ohms. The meter movement itself will have a small resistance which will be part of the total 10K resistance, but it is usually low enough to ignore. The meter in the example below has a resistance of 86 ohms so the true resistor value needed would be 10K-86 or 9914 ohms. ..

3 LED Car battery Indicator

3 LED Car battery Indicator

The operating principle of the circuit is very simple. The first Led D1 is placed in series with the resistor R2 and diode D4.An only be lit this LED indicates that the battery is ypofortismeni. For this reason Led D1 is red. If the voltage is greater than 12V, then netting R5 Z3 turns the transistor TR1, so the glows and Led D2 indicates that the battery of your car is okay and that is why color is green. Now, if the battery voltage exceeds 13,5 V in the same way it lights up and the third LED D3 in the middle of the transistor TR2.Stin cases this increase in voltage is detected by the panel R3 Z1 Z2.Afto means that your battery is yperfortismeni...

Digital Volt and Amp Meter

Digital Volt and Amp Meter

The PIC Microchip Processor must be programmed before it will function as a Volt & Amp meter. There are many internet sites and PIC programmers that you can use. I used a Microchip MPLAB ICD 2 during the project. You might need to made changes to the circuit to accommodate a different type of programmer, do read the programmers instructions carefully. The circuit relies on the internal analogue to digital converter (ADC) of the PIC Microchip Processor. The accuracy is dependant on scaling the input voltage for the ADC for all three measurements. The good news is that both the PIC's which can be used for this project have 10-Bit resolution ADC units which should work adequately in most circumstances...

LED battery voltage monitor

LED battery voltage monitor

An ECU must have a way to monitor battery voltage. Here is a simple op-amp based circuit which will illuminate the LED when the battery voltage drops to a certain level. The turn-on point is set with R2. You must be able to vary Vcc (usually with a good power supply) to set the circuit. Decide at what voltage you'd like the LED to illuminate, and apply this at Vcc. Adjust R2 until the light just illuminates. ..

Low battery indicators with LED

Low battery indicators with LED

For a transistor to conduct, it requires a voltage of about 0.6 between its base and emitter. This voltage is applied from the wiper of the 47K pot. Now if the pot is at minimum, this voltage is across the 22K, so the 47K will have about 1.28v across it - or 1.88 across the pair. Add the 3V9 from the zener: this will require a battery voltage of 5.78v to just turn on the first transistor. Above 5.78 the right hand transistor is turned on, the left hand is therefore off and the LED is also off. Below 5.78v the LED will therefore come on...

Digital Voltmeter with ICL7129ACPL A/D converter

Digital Voltmeter with ICL7129ACPL A/D converter

This 4 1/2-digit DVM circuit is built around a Maxim ICL7129ACPL A/D converter and LCD driver. An ICL8069 CCZR 1.2-V band-gap reference diode is used for a voltage reference. S2a-b-c select one of four ranges up to 200 V (maximum). The meter also has a piezoelectric buzzer for continuity testing. S3 selects either DVM or continuity. Crystal 1 can be changed to 100 kHz if maximum rejection of 50 Hz is desired. The crystal normally provides 120 kHz for best 60-Hz rejection. This is caused by the dual-slope conversion technique used in IC1...

Lead Acid Battery Charger with voltmeter

Lead Acid Battery Charger with voltmeter

This simple circuit makes it posible to monitor the charging process to a higher level. If you need more information then check out the LM3914 Datasheet. Final adjustsments are simple and the only thing needed is a digital voltmeter for the necessary accuracy. Connect an input voltage of 12.65 volt between the positive and negative poles and adjust the 10K trimmer potentiometer until Led 10 lights up. Lower the voltage and in sequence all other Led's will light up. Check that Led 1 lights up at approximately 11.89 volts. ..

LED Voltmeter for Cars

LED Voltmeter for Cars

The circuit, is a comparator, can measure with step of 1Volt, the voltage of battery of car. The clue of voltage become after comparison of voltage of battery, that is applied in the inverting inputs of amplifiers, with voltages of reference that are produced by a Zener D1, the value of which is such so that it present good thermic stability. With the RV1, we regulate the gradation of voltage that we want. The optical clue become from four Led. ..

Digital Car Voltage Meter

Digital Car Voltage Meter

The Car Voltage Gauge is based on 3 parts. The input circuit is an Analog to Digital Converter (IC2 CA3162E). The purpose of this chip is to sample an analog voltage and convert it to a decimal value which is read by a Display/Decoder Driver (IC1 CA3161E). This chip will turn each seven segment display on through the driver transistor Q1 - Q3. The power is derived from the car and is converted to 5 volts by the 5 volt regulator. The circuit works as follows: The 10uf capacitor is charged up by the cars voltage. Its value is then read by IC2 and a decimal value of that voltage is provided to IC1 which multiplexes the three display units. Each display is turned on sequentially with its appropriate value displayed. ..