Friday, January 10, 2014
Battery Saver
A small electronic switch that connects a battery to the equipment for a certain amount of time when a push-button is momentarily pressed. And we have also taken the ambient light level into account; when it is dark you won’t be able to read the display so it is only logical to turn the switch off, even if the time delay hasn’t passed yet. The circuit is quite straightforward. For the actual switch we’re using a well-known MOSFET, the BS170. A MOSFET (T2 in the circuit) used in this configuration doesn’t need a current to make it conduct (just a voltage), which makes the circuit very efficient. When the battery is connected to the battery saver circuit for the first time, capacitor C2 provides the gate of the MOSFET with a positive voltage, which causes T2 to conduct and hence connect the load (on the 9 V output) to the battery (BT1). C2 is slowly charged up via R3 (i.e. the voltage across C2 increases).
This causes the voltage at the gate to drop and eventually it becomes so low that T2 can no longer conduct, removing the supply voltage to the load. In this state the battery saver circuit draws a very small current of about 1 µA. If you now press S1, C2 will discharge and the circuit returns to its initial state, with a new turn-off delay. Resistor R5 is used to limit the discharge current through the switch to an acceptable level. You only need to hold down the switch for a few hundredths of a second to fully discharge C2. In our prototype, connected between a 9 V battery and a load that drew about 5 mA, the output voltage started to drop after about 26 minutes. After 30 minutes the voltage had dropped to 2.4 V. You should use a good quality capacitor for C2 (one that has a very low leakage current), otherwise you could have to wait a very long time before the switch turns off!
The ambient light level is detected using an LDR (R1). An LDR is a type of light sensor that reduces in resistance when the light level increases. We recommend that you use an FW150, obtainable from e.g. Conrad as part number 183547-89. When there is too little light its resistance increases and potential divider R1/R2 causes transistor T1 to conduct. T1 then charges up C2 very quickly through R4, which limits the current to a safe level. This stops T2 from conducting and the load is turned off. The choice of value for R2 determines how dark it has to be before T1 starts to conduct. The battery saver circuit can be added to devices that use 6 or 9 volt batteries and which don’t draw more than 100 mA. The circuit can be built on a piece of experimenter’s board and should be made as compact as possible so that it can be built into the battery powered device.
Copyright : Elektor Electronics
Source: http://www.ecircuitslab.com/2011/06/car-battery-saver-circuit.html
The High Voltage Geiger Counter Supply Circuit Diagram
This High Voltage Geiger Counter Supply Circuit Diagram will generate about 300 volts dc —at a very low current, but enough for a GM tube. be careful with the output.
High Voltage Geiger Counter Supply Circuit Diagram
High Voltage Geiger Counter Supply Circuit Diagram
Thursday, January 9, 2014
Automatic Parking Light For Cars
At night, parking lights make your parked car visible to motorists so they don’t smash into your car. However, these lights drain considerable power out of your car’s battery. Here is a simple, automatic parking light system that works with zero standby current. The circuit is designed to turn on the parking lights automatically for 30 seconds when an approaching vehicle’s light is detected from the rear or front side.
This automatic feature provides safety at night for a parked vehicle. The circuit is built around transistors T1 through T3, MOSFET T4 (BS170) and some discrete components. Darlington photo-transistors T1 and T2 (each L14F1) act as the front and rear sensors. When light from an approaching vehicle falls on the respective photo-transistor, transistor T3 conducts to trigger the gate of MOSFET T4 through R3.
Relay RL1 energises for a period determined by resistor R4 and capacitor C1 and switches on the parking lights (B1 through B4) through its N/O contacts. After the predetermined time elapses, relay RL1 de-energises and the parking lights turn off. Assemble the circuit on a general-purpose PCB and enclose in a suitable case.
Mount the front and rear sensors (photo-transistors T1 and T2) such that these receive light from an approaching vehicle directly, not the ambient light such as street light. Fix 12V bulbs B1 through B4 at an appropriate location in your vehicle or in the parking area.
Continue reading...
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| Automatic Parking Light Circuit Diagram For Cars |
Relay RL1 energises for a period determined by resistor R4 and capacitor C1 and switches on the parking lights (B1 through B4) through its N/O contacts. After the predetermined time elapses, relay RL1 de-energises and the parking lights turn off. Assemble the circuit on a general-purpose PCB and enclose in a suitable case.
Mount the front and rear sensors (photo-transistors T1 and T2) such that these receive light from an approaching vehicle directly, not the ambient light such as street light. Fix 12V bulbs B1 through B4 at an appropriate location in your vehicle or in the parking area.
Telephone Free Indicator
Depending on local regulations and the telephone company you happen to be connected to, the voltage on a free telephone line can be anything between 42 and 60 volts. As it happens, that’s sufficient to make a diac conduct and act like a kind of zener diode maintaining a voltage of 38 V or so. The current required for this action causes the green high-efficiency LED in the circuit to light. Line voltages higher than about 50 V may require R1 to be changed from 10 kΩ to a slightly higher value. When the receiver is lifted, the line voltage drops to less than 15 V (typically 12 V) causing the diac to block and the LED to go out.
The circuit diagram indicates + and – with the phone lines. However, in a number of countries the line polarity is reversed when a call is established. To make sure the circuit can still function under these circumstances, a bridge rectifier may be added as indicated by the dashed outlines. The bridge will make the circuit independent of any polarity changes on the phone line and may consist of four discrete diodes, say, 1N4002’s or similar. Finally, note that this circuit is not BABT approved for connection to the public switched telephone network (PSTN) in the UK.
Continue reading...
Telephone Free Indicator Circuit Diagram
The circuit diagram indicates + and – with the phone lines. However, in a number of countries the line polarity is reversed when a call is established. To make sure the circuit can still function under these circumstances, a bridge rectifier may be added as indicated by the dashed outlines. The bridge will make the circuit independent of any polarity changes on the phone line and may consist of four discrete diodes, say, 1N4002’s or similar. Finally, note that this circuit is not BABT approved for connection to the public switched telephone network (PSTN) in the UK.
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