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You can pick up a 3½-digit digital volt-meter module nowadays for a little as a couple quid. This is a simple and expensive way to fit out a piece of equipment with an instrument. Most modules are based on the well-known ICL7106 IC . They operate from an ordinary 9-V battery, and they only provide a fixed measuring range (200 mV or 2 V). The accessory circuit described here converts a DVM module into a voltmeter with 20-V and 200-V measuring ranges, with the added bonus of automatic range switching. This requires a ground-referenced symmetrical supply voltage (±5 V) instead of a battery. An inexpensive TL431C is also used to generate an adjustable reference volt-age from the supply voltage. The circuit described here uses an LCD module with a fixed measuring range of 200 mV. It has three pins for driving the decimal point; two of them are used here. Automatic Range Switching Schematic This is how the circuit works: IC1 converts the voltage to be measured by the DVM m...

Long Range AM transmitter circuit Diagram The ambit for a able AM transmitter application bowl resonator/filter of 3.587 MHz is presented here. Resonators/filters of added frequencies such as 5.5 MHz, 7 MHz and 10.7 MHz may additionally be used. Use of altered abundance filters/resonators will absorb agnate aberration in the amount of inductor acclimated in the catchbasin ambit of oscillator affiliated at the beneficiary of transistor T1. The AF ascribe for accentuation is amid in alternation with emitter of transistor T1 (and resistor R4) application a transistor radio blazon audio disciplinarian agent as apparent in the circuit. Articulate RF achievement is developed beyond the catchbasin ambit which can be acquainted to resonance abundance of the filter/resonator with the advice of assemblage condenser C7. The abutting two stages formed application low-noise RF transistors BF495 are, in fact, affiliated in alongside for addition of articulate arresting accompanying from beneficiar...

This long-range cordless burglar alarm circuit makes use of a cordless telephone (CLT) unit with paging facility and a few low-cost discrete components. The circuit is so simple that even a novice can easily construct it without any difficulty. When the ‘page’ button on a CLT is pressed and held in that position, the handset starts beeping to indicate that somebody is calling. This function is used here to build the gadget. The system consists of three sub-assemblies:      1. Wireless beeper. The handset of the CLT. 2. Infrared transmitter. A number of IR transmitter circuits based on the well-known 555 chip have been published earlier in EFY. Just select one circuit with a modulating frequency of 36 to 38 kHz and assemble it on a veroboard. After that, enclose it in a proper cabinet. (EFY note. A typical IR transmitter circuit used during testing is shown in Fig. 1.)   3. Infrared receiver-cum-control unit. The circuit diagram of this unit is shown in Fig. 2. Front end of this bloc...

Extending the Range of Ammeters and Voltmeters The ranges of electrical measuring instruments (whether ammeter, voltmeter or any other type of meters) are limited by the currents, which be carried by the coils of the instruments safely. For example, the moving coils of the instruments can carry maximum current of about 50 mA safely and the potential drop across the moving coil is about 50 mV. Hence, it becomes necessary that the current and voltage being measured be reduced and brought within the range of instrument. There are four common devices used for extending the range of the instruments, namely \ 1.        Shunts 2.        Multipliers 3.        Current transformers 4.        Potential transformers The let us discuss the first two topics i.e. shunts and multipliers 1.        Shunts: The range of an ammeters can be extended by connect...

The circuit described here is mostly aimed at development engineers who are looking for an economical step-down converter which offers a wide input voltage range. As a rule this type of circuit employs a step-down converter with integrated switching element. However, by using a more discrete solution it is possible to reduce the total cost of the step-down converter, especially when manufacturing in quantity. The TL5001A is a low-cost PWM controller which is ideal for this project. The input voltage range for the step-down converter described here is from 8 V to 30 V, with an output voltage of 5 V and a maximum output current of 1.5 A. Low-Cost Step-Down Converter With Wide Input Voltage Range Circuit Diagram When the input voltage is applied the PWM output of IC1 is enabled, taking one end of the voltage divider formed by R1 and R2 to ground potential. The current through the voltage divider will then be at most 25 mA: this value is obtained by dividing the maximum input voltage (30 V...