Other gates made with NAND

Source :: http://www.doctronics.co.uk/4011.htm

An important property of NAND gates is that they can be linked to perform the functions of other logic gates. In fact, any logic function can be implemented using only NAND gates:
If you have designed a system which needs a NAND gate, a NOT gate and an AND gate, you might think of using a separate integrated circuit for each logic function. This would leave you with a circuit in which there were three unused NAND gates, five unused NOT gates and three unused AND gates. It is a lot more efficient (and cheaper) to use NAND gates to implement the other functions. All three gates can be made with just one 4011 integrated circuit.

4011 : 2-input NAND gates (easy IC )

Source :: http://www.doctronics.co.uk/4011.htm

Pin connections

The 4011 has four separate 2-input NAND
gates which you can use independently.

Truth table

The truth table of each individual gate is:

input B	input A	output
0	0	1
0	1	1
1	0	1
1	1	0

where '0' represents a LOW voltage, and '1' represents a HIGH voltage.

Dark Activated Switch by IC 741

Source :: http://www.zen22142.zen.co.uk/Circuits/Switching/darksw.htm

Circuit : Andy Collinson
Email: anc@mitedu.freeserve.co.uk

Description:
This circuit will activate a relay when light falls to a preset level. Light level can be adjusted with VR1 and the relay contacts may be used to operate an external light or buzzer.Notes:
The light sensor used is the ORP12 photocell. In bright light the resistance of the ORP12 can be as low as 80 ohm and at 50lux (darkness) the resistance increases to over 1 Mohm. The 1M control should provide a wide range for light intensities, if not its value may be increased. The op-amp senses the voltage difference between pins 2 and 3. The control VR1 is adjusted so that the relay is off, the output of the op-amp will be around 2 Volts. When light falls, the resistance of the photocell increases and the difference in input voltage is amplified by the op-amp, the output will swing towards full supply and drive the transistor and relay. The 270k resistor provides a small amount of hysteresis, so that the circuit switches on and off with slightly different light levels. This eliminates relay chatter. Take great care if you decide to wire the relay to activate a mains lamp. Make sure the relay contacts provide adequate isolation and have ample rating for the load.

Parts List:
ORP12 Photocell (1)
RLY1: 12VSPDT (1)
U1: UA741 (1)
Q1: BC109 NPN (1)
D1: 1N4002 DIODE (1)
F1: 1A (1)
VR1: 1M RESISTOR (1)
ORP12: 500K RESISTOR (1)
R1,R3,R2: 10k RESISTOR (3)
R5: 4.7k RESISTOR (1)
R6: 1k RESISTOR (1)
R4: 270k RESISTOR (1)

CD4001 Light Detector Circuit

Source :: http://www.zen22142.zen.co.uk/Circuits/Switching/ldet.htm
Kindly submitted by Mick Devine from the UK

Notes:
Variable resistor R1 adjusts the light threshold at which the circuit triggers. R1's value is chosen to match the photocells resistance at darkness. The circuit uses a CMOS 4001 IC. Gate U1a acts as the trigger, U1b and c form a latch. S1 resets the circuit. The output device may be a low power piezo buzzer.

555 Timer 5 to 30 Minute

Source :: http://www.zen22142.zen.co.uk/Circuits/Timing/5_30timer.htm


Circuit : Andy Collinson
Email: anc@mitedu.freeserve.co.uk

Descriptipn:
A switched timer for intervals of 5 to 30 minutes incremented in 5 minute steps.

Notes:
Simple to build, simple to make, nothing too complicated here. However you must use the CMOS type 555 timer designated the 7555, a normal 555 timer will not work here due to the resistor values. Also a low leakage type capacitor must be used for C1, and I would strongly suggest a Tantalum Bead type. Switch 3 adds an extra resistor in series to the timing chain with each rotation, the timing period us defined as :-

Timing = 1.1 C₁ x R₁

Note that R₁ has a value of 8.2M with S3 at position "a" and 49.2M at position "f". This equates to just short of 300 seconds for each position of S3. C₁ and R₁ through R₆ may be changed for different timing periods. The output current from Pin 3 of the timer, is amplified by Q1 and used to drive a relay.

Parts List:
Relay 9 volt coil with c/o contact (1)
S1: On/Off (1)
S2: Start (1)
S3: Range (1)
IC1: 7555 (1)
B1: 9V (1)
C1: 33uF CAP (1)
Q1: BC109C NPN (1)
D1: 1N4004 DIODE (1)
C2: 100n CAP (1)
R6,R5,R4,R3,R2,R1: 8.2M RESISTOR (6)
R8: 100k RESISTOR (1)
R7: 4.7k RESISTOR (1)