Circuit knowledge

Showing posts with label meter. Show all posts

Wednesday, September 24, 2014

10 km Long Range Transmitter Circuit 2 meter band

The theoretical circuit is given in Fig. 1 and consists of a Colpitt’s oscillator using 8MHz crystals. Six channels are shown in the schematics—three, in fact, `T were used for the prototype but there is no reason why many crystals cannot be included by using a suitable multiway switch and increasing the number of islands on the board; using the smaller HC25 series crystals would permit more channels to be fitted in the space allotted. The trimmers in series with each crystal allow easy netting to the assigned frequency. The f.m. is applied to the oscillator by a reactance stage, fed by two audio pre-amps. Deviation is con- trolled by a 10kQ potentiometer and the maximum attained on the prototype was 8kHz. Notice the inclusion of decoupling in the audio stages to prevent r.f. pickup so often a cause of poor audio quality in home·constructed equipment. The printed board layout is shown in Fig. 2.

Making PCBs

Cut a piece of single-sided copper board to the size shown and with some {ine abrasive paper, clean the copper surface to remove any oxide or tarnish.

Using a soft, lead pencil, draw out the islands on the board, and then draw around these and the inter- connections of the earth plane edge. The small islands and fine connections are then filled in by means of an etch-resist pen or ine paint brush, using quick drying paint, such as car touch-up paint, thinned down if necessary. The larger areas are then put in care- fully and when the board is dry, each island and connection examined to make sure no copper bridges exist between them. One should also ensure adequate clearances.

Place the board in a suitable plastic or earthen- ware container and pour on just sufficient ferric chloride solution as is necessary to cover it. The solution can be purchased ready-mixed from most radio component stores, or can be made up by a chemist. It is however a corrosive, albeit a mild one, so handle carefully and wash off any of the solution that comes into contact with the skin immediately.

Initially, leave the board submerged for about twenty minutes, agitating occasionally. You will see the chemical action taking place quite clearly and when all the unwanted copper has been eroded, take out the p.c.b., wash in clean water and then dry. Using a wet abrasive pad such as a Brillo pad- the paint is now removed and a final wash and dry will leave the copper gleaming. After a final check of the work, drill the mounting holes for fixing to the metal chassis.

Each board in the transmitter is etched in this way and provided the simple instructions are followed you should easily be able to provide good examples.

Mounting Components

There is no hard-and-fast rule about fixing the components to the board, but the Author favours soldering the resistors first, followed by the capacitors, the coils and finally the transistors. Keep lead lengths short typically 6-12mm for transistors and solder neatly, holding the iron in place just long enough for the solder to flow to the joint. An iron of 15W rating with a bit size of 3mm or so is to be preferred for work of this nature.

Testing the long range transmitter circuit

Connect a 15 volt supply to the board having first established that the polarity is correct and check the voltages shown: a 15 per cent error is quite acceptable, due to component tolerances. With a 6009 microphone and a pair of earphones across C11 to the earth line, check for clean audio and the operation of the deviation control. The oscillator can be tested by connecting a suitable 8MHz crystal in position (i.e. 8-08335MHz for S20-145-5MHz) and listening for the 8MHz signal on a tunable h.f. receiver, coupled loosely to the vicinity of the oscillator stage.

After this feed an audio signal at the input and try to receive this over any standard 2 mtere band receiver unit placed at about 10 meters distance.

With little trial and error you would be able to receive a crystal reception, done! Now you can take the unit to some other far away location and confirm the same.

Friday, September 5, 2014

Simple Meter Impedance speaker Wiring diagram Schematic

A simple impedance meter can be useful to measure the actual impedance of a speaker or headset, ideal for anyone working with sound, making and repairing speakers. This impedance meter works in conjunction with a multimeter or oscilloscope to measure the impedance.

Simple Meter Impedance speaker Circuit Diagram

How to make the measurement of impedance speaker with the multimeter

Connect a digital multimeter to AC voltage in the range of 200mV.
Connect the device under test terminals
SW1 to R7, if the value of the measured impedance is less than 100 ohm R8 or upwards.
With SW2 in the "Set" power-on schema through SW3
Adjust P1 to read exactly 100.0mV the display DVM
Switch SW2 in the "Measure" and read directly from the speaker or headphones impedance value on the display DVM, eg 8.2mV = 8.2 Ohm / 80.1mV = 80.1 Ohm

How to make the measurement of impedance speaker with the oscilloscope:

Connect the oscilloscope instead of DVM (multimeter) and turn P1 fully clockwise.
Short the output speaker and adjust R3 to get a sine wave amplitude of about 2.2V peak-to-peak.
How to make the impedance measurement Speaker "By ear"

Connect a small speaker or headphones, forming a pair of headphones to the output of the schema and turn P1 to obtain a level of sound output moderated. Carefully adjust R3 until the output sound stops, then turn the trimpot to adjust slowly and stop immediately when the sound start again.

List of components

P1 4K7 linear potentiometer
R1 12K 1/4W Resistor
R2 2K2 1/4W Resistor
R3 1K 1/2W Trimmer (cermet)
R4 1K5 1/4W Resistor
4K7 1/4W Resistor R5
R6 3K3 1/4W Resistor
R7 100R 1/4W Resistor (See Notes)
R8 1K 1/4W Resistor (See Notes)
R9 1K 1/4W Resistor (Optional)
22NF 63V Polyester Capacitor C1
C2 330nF 63V Polyester Capacitor
C3 22μF 25V Electrolytic Capacitor
D1, D2 1N4148 75V 150mA Diodes
D3 3mm red LED (Optional)
Q1, Q2, Q3 BC550C 45V 100mA Low noise High gain NPN
IC1 78L05 5V 100mA Regulator IC
SW1, SW2 SPDT Toggle or Slider
SW3 SPST switch or Slider
B1 9V PP3 battery for PP3Clip

Notes:

For very precise measurements using resistors R7 and R8 with 1% or 2% tolerance.
D3 LED pilot and his current limiting resistor R9 are optional.

Sunday, August 24, 2014

ESR Low Resistance Test Meter

As electrolytic capacitors age, their internal resistance, also known as "equivalent series resistance" (ESR), gradually increases. This can eventually lead to equipment failure. Using this design, you can measure the ESR of suspect capacitors as well as other small resistances. Basically, the schema generates a low-voltage 100kHz test signal, which is applied to the capacitor via a pair of probes. An op amp then amplifies the voltage dropped across the capacitor’s series resistance and this can be displayed on a standard multimeter. In more detail, inverter IC1d is configured as a 200kHz oscillator.

Its output drives a 4027 J-K flipflop, which divides the oscillator signal in half to ensure an equal mark/space ratio. Two elements of a 4066 quad bilateral switch (IC3c & IC3d) are alternately switched on by the complementary outputs of the J-K flipflop. One switch input (pin 11) is connected to +5V, whereas the other (pin 8) is connected to -5V. The outputs (pins 9 & 10) of these two switches are connected together, with the result being a ±5V 100kHz square wave. Series resistance is included to current-limit the signal before it is applied to the capacitor under test via a pair of test probes. Diodes D1 and D2 limit the signal swing and protect the 4066 outputs in case the capacitor is charged.

Circuit diagram:

esr-low-resistance-test-meter-schema-diagram1

ESR & Low Resistance Test Meter Circuit Diagram

A second pair of leads sense the signal developed across the probe tips. Once again, the signal is limited by diodes (D3 & D4) before begin applied to the remaining two inputs of the 4066 switch (pins 2 & 3 of IC3a & IC3b). These switches direct alternate half cycles to two 1μF capacitors, removing most of the AC component of the signal and providing a simple "sample and hold" mechanism. The 1μF capacitors charge to a DC level that is proportional to the test capacitor’s ESR. This is differentially amplified by op amp IC4 so that it can be displayed on a digital multimeter – 10Ω will be represented by 100mV, 1Ω by 10mV, etc. To calibrate the schema, first adjust VR1 to obtain 100kHz at TP3.

Next, momentarily short the test probes together and adjust VR4 for 0mV at pin 6 of IC4. That done, set your meter to read milliamps and connect it between TP4 and the negative (-) DMM output. Apply -5V to TP2 and note the current flow, which should be around 2.1mA. Transfer the -5V from TP2 to TP1 and adjust VR2 until the same current (ignore sign) is obtained. Remove the -5V from TP1. Again, set to your meter to read volts and connect it to the DMM outputs. Apply the probes to a 10W resistor and adjust VR3 for a reading of 100mV. Finally, ensure that all capacitors to be tested are always fully discharged before connecting the probes.

Author: Len Cox - Copyright: Silicon Chip Electronics

Wednesday, August 20, 2014

RPM Meter for Automobiles Wiring diagram Schematic

An efficient way to measure the RPM of a vehicle is through its ignition pulses. RPM of a vehicle is directly proportional to the rate of its ignition pulses. An ignition coil (also called spark coil) is an induction coil in an automobile’s ignition system that transforms the battery’s low voltage to the thousands of volts needed to create an electric spark in the spark plugs for igniting the fuel. Here we measure the rate of ignition pulses with a sensor system attached to the spark coil and thus indicate the RPM using a bar graph comprising 20 LEDs.

Circuit and working
Fig. 1 shows the schema for RPM meter. The schema is built around frequency-to-voltage converter LM2917N-8 (IC1), bar display drivers LM3914 (IC2 and IC3), 20 LEDs (LED1 through LED20) and some other components.

Fig. 1: RPM meter schema Diagram

The schema has three stages—pulse detection, frequency-to-voltage conversion and display of voltage by the LED bar graph. To sense the pulses from the ignition coil, 18SWG PVC-covered household wire is wrapped around LT side of the ignition coil. The number of turns should be around 50. Induction pulses from the sensor coil must be reduced, rectified and filtered. Resistor R1 reduces their voltage level, diode D1 rectifies them and capacitor C1 filters them.

These filtered pulses are fed at pin 1 of frequency-to-voltage converter IC1. Voltage output corresponding to the frequency of pulses is available at pin 4 of IC1. The level of this output voltage can be controlled by preset VR1. LM2917N-8 (IC1) is available in 8-pin and 14-pin versions; we have used 8-pin version here. The output of IC1 is fed at pins 5 of IC2 and IC3 through a filter formed by resistor R8 and capacitor C5. This filter removes any variations in the output and provides stable reading. IC2 and IC3 are connected to each other in cascade mode. Pin 9 of both these ICs are held at high voltage to select bar mode.

The number of LEDs glowing will be directly proportional to the input voltage at pin 5, which, in turn, is dependent on the frequency of pulses. This implies that the number of LEDs glowing will be in accordance with the RPM of the vehicle.

The overall system can be calibrated as per one’s liking (see last paragraph). We calibrated it such that each LED indicates about 1200 revolutions. LEDs should be of three different colours so that these can indicate normal (green), medium (blue) and high (red) speed zones.

Power supply is taken from the vehicle’s battery. Car battery’s 12V DC is reduced to 9V so that the display’s brightness remains the same, irrespective of whether the battery is less charged or overcharged.

Fig. 2: An actual-size, single-side PCB for the RPM meter

Fig. 3: Component layout for the PCB

Construction and testing
An actual-size, single-side PCB for the RPM meter is shown in Fig. 2 and its component layout in Fig. 3. After assembling the schema on PCB, enclose it in a suitable box. Use two-pin connectors on the PCB for connecting the sensor coil and the battery terminals.

To check the schema for proper functioning, verify input supply at TP1 with respect to TP0. This supply is reduced to 9 V, which can be checked at TP2. Check the sensed pulses from the ignition coil at TP3 using an oscilloscope. The voltage at TP4 will vary as per frequency of pulses.

To calibrate the system, as we did, use a function generator. Give 20Hz signal at TP3 and, using preset VR1, set its amplitude such that only LED1 glows. When you increase the frequency, you will see more LEDs glowing. Your system is now ready to use. Use preset VR2 to define the frequency range for each LED bar display.

Sourced by: EFY Author: Ashok K. Doctor