Simple Mat Switch Circuit

This simple Simple Mat Switch Circuit Diagram produces a warning beep when somebody crosses a protected area in your home or office. The switch, hidden be-low the floor mat, triggers the alarm when the person walks over it.

The circuit uses a conductive foam as the switch. It can be two small pieces of conductive pads usually used to pack sensitive ICs as antistatic cover. Alternatively, you can make the switch by coating conducting carbon ink on two small pieces of a copper-clad board.

Circuit diagram :

Simple Mat Switch Circuit Diagram

When the circuit is in standby mode, transistor T1 does not conduct, since its base is floating. When the person walks, the switch is pressed and current flows through R1 and the switch to provide positive bias to transistor T1. Transistor T1 conducts and its collector voltage drops, which acts as a negative trigger input for the monostable wired around IC NE555 (IC1).

IC1 outputs a pulse of fifty-seconds duration with preset values of R4 and C3. This pulse is applied to the buzzer through transistor T2. The buzzer sounds a warning beep on unauthorised entry. The pulse duration can be changed to the desired value by changing the values of R4 and C3. Resistor R2 in the circuit makes the trigger pin of IC1 high to prevent false triggering.

Assemble the circuit on a general-purpose PCB and enclose in a plastic case. Use a 9V battery to power the circuit. Connect the touchpad switch with the PCB and hide under the mat at the entrance. The PCB can be mounted on the nearby wall.

Make the switch carefully using conducting foam or copper clad coated with conducting ink. Place the two pieces with their conducting surface facing each other. Solder carefully a thin copper electric wire and ensure that it makes contact when the two plates touch together on pressing. Provide two 1cm rubber tabs between the plates to avoid touch in the standby mode.

Low Power Voltage Doubler Circuit Diagram

All miniature electronic devices operate off batteries. Some of them need higher than the standard battery voltages to operate efficiently. If the battery of that specific voltage is unavailable, we are forced to connect additional cells in series to step up the DC voltage. Thus, the true meaning of miniaturisation is lost. A simple way to overcome this problem is to employ a voltage doubler, if the device under consideration can operate at a small current.

Here we present a low-power voltage doubler circuit that can be readily used with devices that demand higher voltage than that of a standard battery but low operating current to work with. The circuit is quite simple as it uses only a few components. Yet, the output efficiency is 75 to 85 percent along its operating voltage range. The available battery voltage is almost doubled at the output of the circuit.

Here IC1 is wired as an astable multivibrator to generate rectangular pulses at around 10 kHz. This frequency and duty cycle of the pulses can be varied using preset VR1. The pulses are applied to switching transistors T1 and T2 for driving the output section, which is configured as a voltage-doubling circuit. The doubled voltage is available across capacitor C5. During each cycle of the pulse occurance, the high level drives T1 into its saturation, keeping transistor T2 cut off.

Circuit diagram:

Low-Power Voltage Doubler Circuit Diagram

So transistor T1 charges capacitor C4 via the path formed by diodes D2 and D1 to a voltage level slightly lesser than the supply. But during the low period of the pulse, transistor T1 is cut off while transistor T2 is driven into saturation. Now, transistor T2 raises the charge on the negative pole of capacitor C4 by another step equal to the supply voltage. Therefore an equal amount of charging is built up on capacitor C5 via diode D3.

This doubling action increases the total voltage across capacitor C5 to almost double the input voltage. If the output of the pulse generator is maintained with a high enough amplitude and frequency, the output voltage and current remain constant and cater to the needs of the load. Even with the half-wave function, this circuit is almost free of ripple voltage. If the connected load doesn’t require a high current, the efficiency can be expected in the upper 90 percentranges.

Since the input voltage is doubled, the current drain from the input power supply is also doubled at the input but halved at the output. One point of caution is that if the multivibrator’s frequency is fairly high, the output may suffer with the interference imposed over the DC voltage. In this case, the frequency must be set favorably by trials and actual load connection procedure. This tiny circuit can be assembled on the general-purpose PCB. If all of the components are surface-mount type, the whole module can be genuinely miniaturized.

EFY Lab note. During testing with input of 8V and 1.25mA load current the output voltage was found to be around 13V.

Author :M.K. Chandra ,Mouleeswaran And A.N. Vadivudai Naayaki

 

 

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Multitasking Pins Circuit

It’s entirely logical that low-cost miniature microcontrollers have fewer ‘legs’ than their bigger brothers and sisters – sometimes too few. The author has given some consideration to how to economise on pins, making them do the work of several. It occurred that one could exploit the high impedance feature of a tri-state output. In this way the signal produced by the high impedance state could be used for example as a CS signal of two ICs or else as a RD/ WR signal. 

Circuit diagram:

Multitasking Pins Circuit Diagram

All we need are two op-amps or comparators sharing a single operating voltage of 5 V and outputs capable of reaching full Low and High levels in 5-V operation (preferably types with rail-to-rail outputs). Suitable examples to use are the LM393 or LM311.The resistances in the voltage dividers in this circuit are uniformly 10 kilo ohms. Consequently input A lies at half the operating voltage (2.5 V), assuming nothing is connected to the input – or the microcontroller pin connected is at high impedance. 

The non-inverting input of IC1A lies at two thirds and the inverting input of IC1B at one third of the operating voltage, so that in both cases the outputs are set at High state. If the microcontroller pin at input A becomes Low, the output of IC1B becomes Low and that of IC1A goes High. If A is High, everything is reversed.

AVR Dongle Circuit

This circuit is intended to program AVR controllers such as the AT90S1200 via the parallel port. The circuit is extremely simple. IC1 provides buffering for the signals that travel from the parallel port to the microcontroller and vice versa. This is essentially everything that can be said about the circuit. The two boxheaders (K2 and K3) have the ‘standard’ ISP (in system programming) pinout for the AVR controllers. The manufacturer recommends these two pinouts in an attempt to create a kind of standard for the in-circuit programming of AVR-controllers. These connections can be found on many development boards for these controllers. The software carries out the actual programming task.

Circuit diagram :

AVR Dongle Circuit Diagram

It is therefore necessary to have a program (ATMEL AVR ISP), which is available as a free download from http://www.atmel.com. The construction of the circuit will have to made on standard prototype board, since we didn’t design a PCB for this circuit. This should not present any difficulties considering the small number of parts involved. We recommend that inexperienced builders first make a copy of the circuit and cross off each connection on the schematic once it has been made on the board. This makes it easy to check afterwards whether all connections have been made or not.

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