This charger will quickly and easily charge most any lead acid battery. The charger delivers full current until the current drawn by the battery falls to 150 mA. At this time, a lower voltage is applied to finish off and keep from over charging. When the battery is fully charged, the circuit switches off and lights a LED, telling you that the cycle has finished...

This interface circuit provides electrically isolated RS422 communication interface to the PC serial port the isolation circuit protect the PC from direct connection to hazardous voltages...

This page shows two low frequency oscillators that draw ultra low current...

FM reciever with LM386

his coil is home-made. It is actually a single layer 'tapped' air core coil. Please refer to my special section on how to make the DRAIN Coil. Once it is made, the tapped leg goes into the middle hole (Refer to CHART I), but make sure you have the coil positioned so that the tapped leg is closest to the .001uF ceramic capacitor. You will have to bore-out the tapped hole on the PCB a little...in order for the tapped leg to fit. Then solder into place. Start with a two turn tap. If the unit responds well to this...you may want to increase the overall sensitivity of the unit by making a three turn tap. The tap is always closest to the .001uF ceramic disk capacitor. ..

This Design Idea shows how you can use a single-pole momentary-contact switch to select one of three signal sources by scrolling through three output states. The circuit in Figure 1 comprises commonly available components from the CD4000 CMOS-logic series, along with a general-purpose NPN transistor. The total cost of the components doesn`t exceed $1. Only one of circuit`s three outputs, CH1, CH2, or CH3, goes low at any given time, and you can use these outputs to control analog switches, relays, or the gates of JFET switches...

Switching Power Supply 14V

In this small switching power supply, a Schmitt trigger oscillator is used to drive a switching transistor that supplies current to a small inductor. Energy is stored in the inductor while the transistor is on, and released into the load circuit when the transistor switches off. The output voltage is dependent on the load resistance and is limited by a zener diode that stops the oscillator when the voltage reaches about 14 volts...

This circuit uses a couple of Op-amps to produce an interesting sound effect. The left hand CA741 is wired as a standard astable and produces the timing pulses, controlled by C1, R2 and VR1. The output is fed via C2 to the second op-amp and is also direct coupled via the zener ZD1 to Q1. The right hand CA741 is configured as an integrator, its purpose being to distort the output pulse from the first op-amp...

The simple and inexpensive circuit in Figure 1 monitors the liquid level in a container. The piezo crystal, carefully mounted at the bottom surface of the container, receives it activation from the 74HCT14 hex Schmitt trigger. The crystal generates stable clock pulses according to its specification (for example, 6.14 MHz) when it is in free air. The crystal-based clock drives the 0th counter in an 8254 programmable-counter/timer chip, programmed in Mode 0 as an event counter...

Using a product developed for PC-motherboard environmental monitoring, you can configure a low-cost, general-purpose DAS (data-acquisition system) (Figure 1). The DAS can directly monitor multiple voltage channels as well as temperature and frequency. It can also directly monitor digital sensors. Using only a few additional components, the system can accommodate other sensor and transducer elements. The flexibility exists to expand the scheme to cover additional input channels if necessary. For voltage sensing, the ADM9240 contains a multichannel ADC that can directly monitor as many as six input channels...

To add tones or shades of the main colors to the tricolor LED, you do not need to modify the circuit in Figure 1; you need only consider the software. Software modifications consist of adding more color planes or pages of display buffer, adding memory locations (mapped onto the LED dots), and increasing the number of refresh times, in which the controller updates all LED dots to cover all added color planes. For example, if you decide to use four color planes, divided into two red and two green planes, for dot i of the dot-matrix LED, you`ll obtain the shades listed in Table 1...

Detection for trains on model railway

This light valve can be used for example to detect trains on model railway or a lap counter at the close racing. D3 receives a constant stream of power built around T1. When the light beam from D3 to T3 is not interrupted, led T3 and T2 is the basis of practically grounded. T2 not conduct and the LED is not lit. When the beam is interrupted, spert T3 and T2 conducts and the LED will light. Of course listen to other things like LED control between plus and the collector of T2. Please note the maximum load of 100 mA. The supply voltage may be between 4.5 and 12 volts...

Infra-red detector circuit

This circuit is a simple IR detector for testing IR remote controllers. The circuit is based on one phototransistor which receives the IR beam. The NPN transistor works as an amplifier which feeds current to the led. When this circuit detects IR or light, the LED is on. So you need to shield the phototransistor from ambient light if you don't want to do your tests in the dark. The best way is to fit the phototransistor in a small black tube. I used 2 cm long piece of insulating tube and fitted the phototransistor into the middle of the tube...

At some stage, we will all find ourselves pushing hi-fi equipment just a little too hard, and if lucky, will just find that the sound has become "dirty". If this happens too often or is too severe, tweeters are the first to go - they are damaged by the excessive power generated by a combination of "power compression" and the harmonics created when an amplifier clips...

10Watt HI-FI Amplifier (TDA2002)

A very small but good quality amplifier circuit that is also fairly cheap. It is based on TDA2002 which offers very low distrortion. Power should be 12-15 volt 1,2A. The amplifier frequency responce ranges from 40Hz to 15Khz. A good heatsink is required. At the input you can connect your mp3 player or your pc audio out etc...

The circuit in Figure 1 provides a remote menu-selection switch matrix for PCs. It connects a linear, 8-bit switch to the RS-232C port; the RS-232C signal pins provide the circuit`s frugal power requirements. You can easily modify the circuit to read more switch inputs. The heart of the circuit is a 74HC165 8-bit, serial-output shift register...