To attention of readers the indicator of the battery state, signaling flow of light and sound signals on its discharge, when the voltage will decrease below the threshold level. The device is assembled on the basis of detector low voltage series CR.
Described in the article, the device belongs to the group of simple indicators which only indicate a decrease in the voltage on the battery (AB) below the specified limits. Easier proposed indicator can be considered only a device consisting of a Zener diode, led and resistor, but it has inverted indication, i.e. turns off when the voltage on AB less than the threshold.
The basis of the proposed discharge indicator AB - detector low voltage - IC series CR. These chips are specially designed to monitor the reduction of the supply voltage in microprocessor technology and is ideally suited for the decision of a task.
The composition of the chip includes a reference voltage source, comparator, comparing the voltage model, and the output transistor with an open collector. It is made in a three-terminal, "transistor", body CT-26. For implement the basic indicator it is sufficient to connect the output circuits the led and current limiting resistor. The size of such devices almost equal dimensions of the chip and LEDs (resistor, you can take the a miniature). The only drawback of this indicator is rigidly fixed a number of manufactured chips in this series, each of which designed for a very specific threshold voltage.
The last two digits in the name of each chip series indicate its threshold switching voltage. The main characteristics are given in the table.
Fixed threshold voltage enable although they create some difficulties but still provide indicators of different discharge AB. For example, chip CSP threshold voltage of 2 V can be done very compact indicator for devices powered by two Nickel-cadmium batteries (toys, cameras, music players, radios, lights, etc.).
Such an indicator can be supplemented with a simple audible alarm. The scheme is one of variants of such a device is shown in Fig. 1.
The use of SHOP allows the chip to obtain high efficiency and large the range of working voltage. Almost to redo the indicator under another the voltage is enough to put a chip series CR with a different threshold voltage. The only exception is CROP, since the voltage of 2 V the generator on the chip K561LN2 not working. However, this is easily explained. For chipset series C interval of the supply voltage is 3...15 V. On practice this generator worked steadily to 2.5 V, but with reduced volume of the signal. Current consumption indicator off state (the led is off, no beeps) at a voltage of 6 not In greater than 20 μa, and when on, the led is on, the alarm device emits tone of the parcel) at a voltage of 5.2 V - 6 mA.
So low quiescent current in off state allows you to embed the indicator in the device requiring the continuous monitoring of the voltage on AB. When this, it must be connected to the power switch device, directly on the battery terminals.
Circuit Board indicator unilaterally made of foil fiberglass. Its drawing is shown in Fig. 2. It was developed under the common elements and therefore has an increased size. When using chip series 564 and other details for surface installation you can get much more compact design. To reduce dimensions instead of a piezoceramic emitter RFP-18, it is desirable to apply more miniature with an acceptable volume. Other parts - resistors MLT, OMLT, C2-OPA, etc. with a capacity of 0.125 watts. The capacitor C1 is any oxide with minimal leakage current, and the rest - K10-17, or km. The diodes may be possible to apply from the series KD522, KD521. Led - any with a rated current not exceeding 10 mA. It color, brightness and size can be chosen according to specific conditions.
The establishment of the indicator is reduced to the selection of the resistor R6 to provide the maximum volume of the applied system.
Generally, the indicator can be applied to any sounder. Main requirements - minimum current consumption in the off state and performance at the required threshold voltage. Acceptable use and acoustic radiator with a built-in generator, for example, NRMA firm JL World.
Author: S. Malakhov, St. Petersburg