Amatuer Electronic circuit designs....

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Non-Isolated Battery Charger

Using this circuit will give Good Charging results to a Sealed Lead Acid Battery, like I use in the Metal Detector.

It is Extremely Small in size and has a low parts count, making it ideal in some situations. It can also be adapted for Charging Ni cads.

This charger is both Current and Voltage Regulated.


The Output is short circuit protected.

The 1 Ohm resistor is a Fusing Resistor, Protecting the battery in case a short occurs.

With the 2.2 ufd capacitor it will produce an output of about 100 Ma. A capacitor of 1 ufd will produce an output of about 50 Ma.

The Zener used here, is rated at: 14 Volt and 5 Watts. I do not recommend a lower wattage than this.

A HV Arc Circuit

A Very Low Current, High Voltage Spark, that is "Manually Triggered"

Although its not easily Measured, the Peak Ouput voltage will be over 5,000 Volts.

T1 is a small audio transformer and it steps up the voltage to about 500 Volts at Point "X" on the schematic.

The main power limitation to this device is T2.
It can be a Standard Trigger Coil, like those used on Strobe Kits, or a Custom made Trigger Coil.

For A Custom coil, You can wind one Simular to those in my Stun Gun Write-ups.

Which-Ever Coil you use for T2, If you try for Too long of an Arc, It will Arc Internally, Permanently Shorting itself Out.

So Start with a Small Arc and Slowly Increase it to try and find the Maximum Distance.
Than Reduce it Slightly to give a small Safety Margin.

555 Negative Voltage Generator

This circuit is supplied as a hobby project. I get frequent requests for help indicating that there is often a need to generate a negative voltage for RS-232 type interfaces or other circuits when there is only a +5 or +12 volt source that is readily available. I have encountered the same problem. There are commercially available answers for such problems but they are usually cumbersome, expensive, not readily available when you need them, and they are not really adaptable to all situations.
For me, the solution came in the form of a 555 IC project back in the late 70s and early 80s. It is for all practical purposes, a quickie negative voltage generator. There is nothing new or particularly clever about the design as it is based on one of the most popular and versatile ICs ever produced. The parts are plentiful and cheap, two of my hobby criteria for projects; usually they are all part of any electronics workshop junk box. The circuit is very straight forward and easily adaptable to various requirements. The circuit can be used to generate twice the supply voltage by reversing the polarity of the diodes and the output capacitor.

Automotive Brake Lights Flasher

This circuit is supplied as a hobby project. In this case, check with the Highway Patrol or Department Of Safety to make sure that this is legal in your state. The 555 timer IC is connected for astable multivibrator operation. This is a flasher circuit modified to turn on and off a bulb instead of a LED. It will create a flashing condition on the brake lights while the brake is pressed. (Normally when depressed, the brake lights stay on but do NOT flash.) The flashing rate, for the attention of drivers behind you, can be varied from very fast to a maximum of once in 1.5 seconds by varying the preset variable resistor VR1. (You might also wish to see our Astable 555 Square Wave Calculator.) The ON time of the circuit is given by the formula T(ime) ON = 0.69 x C1 x (R1 + VR1) seconds and the OFF time is T(ime) OFF = 0.69 x C1 x VR1 seconds.
You can increase the value of C1 in varied values to 100uF to get a slower flashing rate of up to once in 10 seconds.

Gate Alarm

Figure 1 represents a cheap and simple Gate Alarm, that is intended to run off a small universal AC-DC power supply.

IC1a is a fast oscillator, and IC1b a slow oscillator, which are combined through IC1c to emit a high pip-pip-pip warning sound when a gate (or window, etc.) is opened. The circuit is intended not so much to sound like a siren or warning device, but rather to give the impression: "You have been noticed." R1 and D1 may be omitted, and the value of R2 perhaps reduced, to make the Gate Alarm sound more like a warning device. VR1 adjusts the frequency of the sound emitted.

IC1d is a timer which causes the Gate Alarm to emit some 20 to 30 further pips after the gate has been closed again, before it falls silent, as if to say: "I'm more clever than a simple on-off device." Piezo disk S1 may be replaced with a LED if desired, the LED being wired in series with a 1K resistor.

Figure 2 shows how an ordinary reed switch may be converted to close (a "normally closed" switch) when the gate is opened. A continuity tester makes the work easy. Note that many reed switches are delicate, and therefore wires which are soldered to the reed switch should not be flexed at all near the switch. Other types of switches, such as micro switches, may also be used.

Modular Burglar Alarm

This circuit features automatic Exit and Entry delays and a timed Bell Cut-off. It has provision for both normally-closed and normally-open contacts, and a 24-hour Personal Attack/Tamper zone. It is connected permanently to the 12-volt supply and its operation is "enabled" by opening SW1. By using the expansion modules, you can add as many zones as you require; some or all of which may be the inertia (shock) sensor type. All the green LEDs should be lighting before you open SW1. You then have up to about a minute to leave the building. As you do so, the Buzzer will sound. It should stop sounding when you shut the door behind you. This indicates that the Exit/Entry loop has been successfully restored within the time allowed. When you re-enter the building you have up to about a minute to move SW1 to the off position. If SW1 is not switched off in time, the relay will energise and sound the main bell. It will ring for up to about 40 minutes. But it can be turned off at any time by SW1. The "Instant" zone has no Entry Delay. If you don't want to use N/O switches, leave out R8, C8 and Q2; and fit a link between Led 3 and C7. The 24 Hour PA/Tamper protection is provided by the SCR/Thyristor. If any of the switches in the N/C loop is opened, R11 will trigger the SCR and the bell will ring. In this case the bell has no time limit. Once the loop is closed again, the SCR may be reset by pressing SW2 and temporarily interrupting the current flow. The basic circuit will be satisfactory in many situations. However, it's much easier to find a fault when the alarm is divided into zones and the control panel can remember which zone has caused the activation. The expansion modules are designed to do this. Although they will work with the existing instant zone, they are intended to replace it. When a zone is activated, its red LED will light and remain lit until the reset button is pressed. All the modules can share a single reset button.

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