This solar charging controller is connected between a solar cell 12V= (open circuit voltage 14…22V=) and an accumulator 12V= to prevent an overcharge of the accumulator. LED displays for “accu full” (approx. 14.4V=) and “charging”. Own power consumption < 2.5 mA.

Allows to regulate the charging of a Lead acid battery, to optimise efficiency

Indicate charging, or when battery is fully charged

Product Photo

Technical data:

• Input voltage: solar cell panels: 14…22V= open circuit voltage, nominal voltage: 12V=
• Max. input current: 6 A, short-time till 5 min: 10 A
• Inrush voltage: battery voltage < approx. 13.4V
• Interrupting voltage: battery voltage > approx. 14.4V
• Displays: 1 LED for “Charging”, 1 LED for “Accu full”
• Own power consumption: < 2.5 mA (LED switched on)
• Dimensions: approx. 72 x 50 x 42 mm(without fixing straps)

The circuit consists of two identical halves and is called a Flip Flop because one half is ON while the other half is OFF. The ON half is keeping the OFF half OFF but it cannot keep it off indefinitely and gradually the OFF half turns ON via the 10k base-bias resistor.
This drives the ON side OFF and the circuit changes state. In other words it flips over. The same events occur in the other half of the cycle and the circuit eventually flops back again.

This sounds very complicated but in reality the circuit is quite simple in operation as one half is exactly the same as the other and there’s only 5 components in each half.

This circuit uses just one IC and a very few number of external components. It displays the audio level in terms of 10 LEDs. The input voltage can vary from 12V to 20V, but suggested voltage is 12V.

The LM3915 is a monolithic integrated circuit that senses analog voltage levels and drives ten LEDs  providing a logarithmic 3 dB/step analog display. LED current drive is regulated and programmable, eliminating the need for current limiting resistors.

The IC contains an adjustable voltage reference and an accurate ten-step voltage divider. The high-impedance input buffer accepts signals down to ground and up to within 1.5V of the positive supply. Further, it needs no protection against inputs of ±35V. The input buffer drives 10 individual comparators referenced to the precision divider. Accuracy is typically better than 1 dB.

This circuit produces a sound similar to the police siren.
It makes use of two 555 timer ICs used as astable multivibrators. The frequency is controlled by the pin 5 of the IC.
The first IC (left) is wired to work around 1Hz. The 47uF capacitor is charged and discharged periodically and the voltage across it gradually increases and decreases periodically.
This varying voltage modulates the frequency of the 2nd IC. This process repeats and what you hear is the sound remarkably similar to the police siren.

Two presets VR1 and VR2 are provided to vary the siren period of repetition and the tone of the siren.
By varying VR1 you can set how fast the siren changes from high freq. to low freq.
VR2 sets the siren frequency. Adjust VR1 and VR2 to suit your taste.

This is basically a flasher circuit modified to turn on and off a bulb instead of a LED. It uses a 555 timer IC working as an astable multivibrator. The flashing rate can be varied from very fast to a maximum of once in 1.5 sec by varying the preset VR1.
The ON time of the circuit is given by:
TON= 0.69xC1x(R1 + VR1) second

and the OFF time is:
TOFF= 0.69xC1xVR1 second

You can increase the value of C1 to 100uF to get a slower flashing rate of upto once in 10 sec.

Description:
A circuit that offers visual indication of fluid level in a vessel, with a switchable audible alarm. Example uses would be to monitor the level of water in a bath or cold storage tank.

The Conductance of Fluids
Conductance is the reciprocal of resistance. The conductance of fluids vary with temperature, volume and separation distance ofthe measurement probes. Tap water has a conductance of about 50 uS / cm measured at 25°C. This is 20k/cm at 25°C. See this site for more details about the conductance of fluids.

Circuit Notes
This circuit will trigger with any fluid with a resistance under 900K between the maximum separation distance of the probes. Let me explain further. The circuit uses a 4050B CMOS hex buffer working on a 5 volt supply. All gates are biased off by the 10M resistors connected between ground and buffer input. The “common” probe the topmost probe above probe 1 in the diagram above is onnected to the positive 5 volt supply. If probe 1 is spaced 1 cm away from the common probe and tap water at 25 C is detected between the probes (a resistance of 20k) then the top gate is activated and the LED 1 will light. Similarly if probe 2 at 2 cm distance from the common probe detects water, LED 2 will light and so on. Switch 1 is used to select which output from the hex buffer will trigger the audible oscillator made from the gates of a CMOS 4011B IC.

Placement of Probes
As 7 wires are needed for the probe I reccommend the use of 8 way computer ribbon cable. The first two wires may be doubled and act as the common probe wire. Each subsequent wire may be cut to required length, if required a couple of millimetres of insulation may be stripped back, though the open “cut off” wire end should be sufficient to act as the probe. The fluid and distance between probe 6 and the common probe wire must be less than 900k. This is because any voltage below 0.5 Volt is detected by the CMOS IC as logic 0. A quick potential check using a 900k resistance and the divider formed with the 10M resistor at the input proves this point:
5 x (0.9 / (0.9+10) = 0.41 Volt

As this voltage is below 0.5 volt it is interpreted as a logic 0 and the LED will light. If measuring tap water at 25 C then the distance between top probe and common may be up to 45 cm apart. For other temperatures and fluids, it is advisable to use an ohmmeter first. When placing the probes the common probe must be the lowest placed probe, as the water level rises, it will first pass probe 1, then 2 and finally probe 6.

Description:
This is a complete alarm system with 5 independent zones suitable for a small office or home environment. It uses just 3 CMOS IC’s and features a timed entry / exit zone, 4 immediate zones and a panic button. There are indicators for each zone a “system armed” indicator. The schematic is as follows:

 
Please Note: This diagram is drawn with Relay and Switch Contacts labeled as in my Practical Section

Wheres the Parts List ? On the diagram click here for more info.

 
Circuit Notes
Each zone uses a normally closed contact. These can be micro switches or standard alarm contacts (usually reed switches). Suitable switches can be bought from alarm shops and concealed in door frames, or window ledges.

Zone 1 is a timed zone which must be used as the entry and exit point of the building. Zones 2 – 5 are immediate zones, which will trigger the alarm with no delay. Some RF immunity is provided for long wiring runs by the input capacitors, C1-C5. C7 and R14 also form a transient suppressor. The key switch acts as the Set/Unset and Reset switch. For good security this should be the metal type with a key.

Operation
At switch on, C6 will charge via R11, this acts as the exit delay and is set to around 30 seconds. This can be altered by varying either C6 or R11. Once the timing period has elapsed, LED6 will light, meaning the system is armed. LED6 may be mounted externally (at the bell box for example) and provides visual indication that the system has set. Once set any contact that opens will trigger the alarm, including Zone 1. To prevent triggering the alarm on entry to the building, the concealed re-entry switch must be operated. This will discharge C6 and start the entry timer. The re-entry switch could be a concealed reed switch, located anywhere in a door frame, but invisible to the eye. The panic switch, when pressed, will trigger the alarm when set. Relay contacts RLA1 provide the latch, RLA2 operate the siren or buzzer.

Circuit Notes
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 microswitches, may also be used.

Description
In this circuit a non-locking push switch is used to activate a load. The load remains switched on until power is removed from the circuit.

Circuit Notes:
The load is represented by R5 and D1, but could be a lamp, a relay or another circuit. S2 breaks power to the circuit but could be omitted altogether. If S2 is left out, then reset would be by disconnecting the power; this would mean unplugging the battery if battery powered or disconnecting from the electrical outlet.

When first plugged in (or S2 is operated) C1 charges via the base emitter junction of Q1 and hence a brief positive pulse is applied. Q1 will switch on and be saturated, its collector emitter voltage being close to zero volts. Q2 is therefore off, and the full supply voltage is applied to Q1 base via D1, R5 and R1. The circuit is now in a permanent off state.

If S1 is momentarily pressed, a high voltage is applied to Q1 collector and also Q2 base via R3. Q2 now becomes saturated and the full power to the load is applied. At the same time Q2 collector voltage is now low, and so the volatge at Q1 base, applied via R1 is also low and Q1 switches off. As Q1 is off, bias for Q2 is obtained via R2 and R3 and the circuit is now permanently latched on. Even if S1 is pressed again, this has no effect. The only way to reset is to use S2 (if fitted) or remove power source.

The transistor choice depends on the load. For low currents up to 100mA QN2222 transistors or any other general purpose transistor may be used. For higher voltages and currents, the load can be a relay, its contacts rated for the chosen load.

Description
This circuit for an electronic night light was submitted by Adam from Canada. I have provided the notes.

Circuit Notes
The two transistors are used as a direct coupled switch, Adam used 2SC711 but any general purpose transistor will do e.g. 2N3904, BC109C. The CDS photocell, type ORP12 is normally illuminated, therefore its resistance is low. The 50k control, the 1k resistor and the photocell form a potential divider which biases the first transistor. This transistor is on, its collector being held low, turns the last transistor and hence lamp and relay off.

In darkness, the resistance of the photocell becomes high and the first transistor switches off. The base voltage for the second transistor goes high, switching this transistor on and illuminating the lamp. Although Adam used a secondary supply of 3V , you could use any voltage and any lamp here. Make sure the relay contacts can handle the load. If using a large relay, it is preferable to wire a 1N4001 in reverse polarity across the coil. This will prevent the back EMF of the relay from damaging the transistors.