IR Remote-Control Checker
Suitable for any Infra-red emitting device
3V battery supply
Circuit diagram:
Parts:
R2______________47R 1/4W Resistor D1______________LED (Any dimension, shape and color) Q1____________Infra-red Photo Transistor (Any cheap type) Q2____________BC327 45V 800mA PNP Transistor SW1____________SPST Toggle or Slide Switch (Optional, see Note) B1_______________3V Battery (2 x 1.5V AA, AAA or smaller type Cells in series)
Comments:
A very simple device allowing a quick check of common Infra-red Remote-Controls can be useful to the electronics amateur, frequently asked to repair or test these ubiquitous devices.A reliable circuit was designed with a handful of components: the LED will flash when any of the Remote-Control pushbuttons will be pressed. The side of the Remote-Control bearing the IR emitting diode(s) must be directed towards the Photo Transistor (Q1) of the checker circuit: maximum distance should not exceed about 20 - 25cm.
Note:
- Current drawing of the circuit is less than 1mA when the LED illuminates and 0mA when no signal is picked-up by the Photo Transistor: therefore, SW1 can be omitted.
Water-level Indicator
Water reservoir automatic level control
Simple circuitry - 12V supply
Circuit diagram:
Parts:
R1,R2___________15K 1/4W Resistors
R3______________10K 1/4W Resistor
R4_______________1K 1/4W Resistor
D1______________LED any type and color
D2___________1N4148 75V 150mA Diode
IC1____________4001 Quad 2 Input NOR Gate CMos IC
Q1____________BC337 45V 800mA NPN Transistor
SW1____________SPDT Toggle or Slide Switch (Optional)
RL1___________Relay with SPDT 2A @ 230V switch
Coil Voltage 12V - Coil resistance 200-300 Ohm
Two steel rods of appropriate length
Device purpose:
By means of a Relay, employed to drive a water pump, this circuit provides automatic level control of a water reservoir or well.Circuit operation:
The shorter steel rod is the "water high" sensor, whereas the longer is the "water low" sensor. When the water level is below both sensors, IC1C output (pin #10) is low; if the water becomes in contact with the longer sensor the output remains low until the shorter sensor is reached. At this point IC1C output goes high, Q1 conducts, the Relay is energized and the pump starts operating. Now, the water level begins to decrease and the shorter sensor will be no longer in contact with the water, but IC1C output will be hold high by the signal return to pin #5 of IC1B, so the pump will continue its operation. But when the water level falls below the longer sensor, IC1C output goes low and the pump will stop.SW1 is optional and was added to provide reverse operation. Switching SW1 in order to connect R3 to pin #11 of IC1D, the pump will operate when the reservoir is nearly empty and will stop when the reservoir is full. In this case, the pump will be used to fill the reservoir and not to empty it as in the default operating mode.Notes:
- The two steel rods must be supported by a small insulated (wooden or plastic) board.
- The circuit can be used also with non-metal tanks, provided a third steel rod having about the same height of the tank will be added and connected to the circuit's negative ground.
Temperature-controlled 12V dc Fan
Suitable for computer cooling fans
LED motor speed indicator
Circuit diagram:
Parts:
R1______________15K @ 20°C n.t.c. Thermistor (See Notes) R2_______________1K5 1/4W Resistor (See Notes) R3_______________1K 1/4W Resistor R4_____________270R 1/4W Resistor R5______________22K 1/2W Trimmer Cermet or Carbon R6_____________680R 1/4W Resistor (Optional, see Notes) R7_____________470R 1/2W Trimmer Cermet or Carbon (Optional, see Notes) C1_____________100µF 25V Electrolytic Capacitor D1______________LED (Optional, any shape and color, see Notes) Q1____________BC547 45V 100mA NPN Transistor Q2____________BD140 80V 1.5A PNP Transistor M1____________Fan Motor 12V 700mA max.
Comments:
Requested by some correspondents, this simple design allows an accurate speed control of 12V dc fan motors, proportional to temperature. A n.t.c. Thermistor (R1) is used as temperature sensor, driving two directly coupled complementary transistors wired in a dc feedback circuit. An optional circuitry was added to remotely monitor fan operation and to allow some sort of rough speed indication by means of the increasing brightness of a LED.Notes:
- R5 must be set to allow motor just starting at the desired temperature.
- Any n.t.c. Thermistor in the 6K8 - 22K range value might work, provided R2 value is one/tenth of Thermistor's value.
- R6, R7 and D1 are optional: R7 must be adjusted until the LED glows faintly when the motor is just running.
Fridge door Alarm (2nd Version)
Alternative version of the popular circuit
3V battery supply - Still operating at 1.3V
Circuit diagram:
Parts:
R1______________10K 1/4W Resistor R2_____________Photo resistor (any type) R3_______________2M2 1/4W Resistor R4_______________1M 1/4W Resistor C1______________10µF 25V Electrolytic Capacitor C2_____________100nF 63V Polyester Capacitor D1____________1N4148 75V 150mA Diode IC1,IC2_________7555 or TS555CN CMos Timer ICs BZ1___________Piezo sounder (incorporating 3KHz oscillator) B1____________3V Battery (2 x 1.5V AA, AAA or smaller type Cells in series)
Comments:
The main purpose of this design was to obviate a small defect of the very popular Fridge Door Alarm circuit, available on this website since 1999 and built by a lot of hobbyists. Unfortunately, that circuit stops operating when the battery voltage falls below about 2.6 - 2.7 Volts. This is due to the 4060 CMos IC used. In some cases, devices made by some manufacturers (but not Motorola's) fail to operate even at nominal 3V supply voltage. A simple cure to this shortcoming could be the substitution of the original IC specified with a 74HC4060 chip: this should allow circuit operation down to 2V but, unfortunately, this IC is not easy to locate. For this reason, an equivalent circuit using about the same parts counting was developed, in order to allow safe operation even when battery voltage falls down to about 1.3V.Circuit operation:
The circuit, enclosed in a small box, should be placed in the fridge near the lamp (if any) or close to the opening. With the door closed, the interior of the fridge is in dark, the photo resistor R2 presents a high resistance (>200K) thus clamping IC1 by holding C1 fully charged across R1 and D1. When a beam of light enters from the opening, or the fridge lamp lights, the photo resistor lowers its resistance (<2K) stopping C1 charging current. Therefore IC1, wired as an astable multivibrator, starts oscillating at a very low frequency and after a period of about 24 sec. its output pin (#3) goes high, enabling IC2. This chip is also wired as an astable multivibrator, driving the Piezo sounder intermittently at about 5 times per second. The alarm is activated for about 17 sec. then stopped for the same time period and the cycle repeats until the fridge door closes.Notes:
- Delay time can be varied changing C1 and/or R3 values.
- Beeper repetition rate can be varied changing C2 and/or R4 values.
- Stand-by current drawing: 150µA.
- Place the circuit near the lamp and take it away when defrosting, to avoid circuit damage due to excessive moisture.
- Do not put this device in the freezer.
