DS

In networks, the supremacy of coax cable is a thing of the past. Nowadays, Ethernet connections are made using UTP cables. The BNC plug has yielded to the 8-way RJ45 plug. Previously, coax cables were daisy-chained from computer to computer and terminated at the two ends using 50-_ resistors, but modern networks use central ‘socket boxes’ (switches and/or hubs) to interconnect everything. The connections between the hubs and the computers are made using patch cables having the same sequence of leads in the RJ45 connectors at each end. For making a direct connection between two computers without using a hub or switch, a ‘crossover cable’ is used. Such a cable has the leads cross-linked in order to allow the two computers to directly communicate with each other. If there are problems with the network, it can be handy to be able to directly interconnect twocomputers, or directly connect a computer to a cable or ADSL modem without using a hub or switch. A long crossover cable is not always...

The Maxim MAX 6665 (www.maxim-ic.com) provides a complete temperature-dependent fan controller. It can switch fans operating at voltages of up to 24 V and currents of up to 250 mA. The IC is available from the manufacturer in versions with preset threshold temperatures between +40 °C (MAX6665 ASA40) and +70 °C (MAX6665 ASA 70). The device’s hysteresis can be set by the user via the HYST input, which can be connected to +3.3 V, connected to ground, or left open. The following table shows the hysteresis values available: HYST = Hysteresis open = 1 °C ground = 4 °C +3.3V = 8 °C Circuit diagram: Fan Controller Circuit Diagram The other pins of the SO8 package are the FORCEON input and the status outputs WARN, OT and FANON. The test input FORCEON allows the fan to be run even below the threshold temperature. The open-drain output WARN goes low when the temperature rises more than 15 °C above the threshold temperature, while the open-drain output OT indicates when the temperature is mo...

Have you ever connected two PCs together via modems using a twisted pair cable and nothing happened? That’s because the modems are expecting a phone line with all the signals and voltages supplied by the local telephone exchange. This circuit simulates the DC power and signal isolation but not the "dial tone" or the "ring signal". It suffices to connect two PCs together to communicate and exchange files using HyperTerminal. The circuit is self-explanatory and needs only one power supply for both modem lines. Although 50V DC is the usual exchange line voltage, this circuit should operate down to 20V. A 600O line transformer (eg. Jaycar cat. MM-1900) provides signal isolation, while the resistors provide current limiting and keep the lines as balanced as possible. Circuit diagram: How To Connect Two PCs Using Modems Circuit Diagram When using this set-up with HyperTerminal, you should not select a Windows modem driver in the "Connect To" dialog. Instead, con...

This simple circuit aims to provide an indication of an appliance if it is ON or OFF with the use of green and red LEDs. BC337 – a small signal NPN Silicon AF medium power transistor used for general purpose switching and amplifying applications with features such as TO-18 manufactured package, suited for AF driver stages and low power output stages, and divided into three group types. Single Pole Single Throw (SPST) – a single on-off switch where the two terminals are either connected together of not connected to anything The indication produced by the LEDs could mean that the red LED will illustrate that the equipment is turned ON while the green LED will illuminate upon turning OFF the same appliance. It could also be the other way around since green normally signifies that there is life on an equipment. This is applicable with any appliance that is powered and operated by AC mains which can be 230 V or 115 Vac. A suitable switch SW1 made of single pole single throw type will be cap...

Most often a motor is controlled from two locations as shown in figure below. The stations are station 1 and station 2. The motor M can be started and stopped from the push buttons located in the circuits of the  “Two Station Motor Control”  is shown in figures below. (A) Control circuit of the two Station Motor Control (B) Power circuit of the Two Station Motor Control Control Operation The start and stop operation of the  “Two Station Motor Control”  is the same as the start and stop operation of the  “Across The Line Magnetic   Starter”  except the two stop and two start push button are used in the two station motor. The two stop push button are connected in series while the two start push button are connected in parallel. Pressing any one of the two start push button will complete the current flow L1, O.L. (95-96), stop push button station 1. Stop push button station 2, contacts (3-4) of either any one of the start push buttons at station 1 or 2, contactor C to line L2. This will e...

Here are two simple 12V DC motor speed controllers that can be built for just a few dollars. They exploit the fact that the rotational speed of a DC motor is directly proportional to the mean value of its supply voltage. The first circuit shows how variable voltage speed control can be obtained via a potentiometer (VR1) and compound emitter follower (Q1 & Q2). With this arrangement, the motor’s DC voltage can be varied from 0V to about 12V. This type of circuit gives good speed control and self-regulation at medium to high speeds but very poor low-speed control and slow starts. The second circuit uses a switchmode technique to vary motor speed. Circuit diagram: Fig.1: a very simple motor speed controller based on a compound emitter follower (Q1 & Q2). Here a quad NOR gate (IC1) acts as a 50Hz astable multivibrator that generates a rectangular output. The mark-space ratio of the rectangular waveform is fully variable from 20:1 to 1:20 via potentiometer VR1. The output from ...

If the frequency of operation of pumping liquid into a tank is to frequent, too much stress is subjected to a single motor pump. In such case the life span of the motor may not last long. To avoid to much stress to a single motor pump, it is wise to add another motor pump. The two motor are design to operate alternately. Figure (A) illustrate two motor pumps that alternately pumps liquid into tank. Control Operation Figure (B) illustrate the schematic diagram of the control circuit of the “Alternate Operation of a Two Motor Pump”. Closing the toggle switch SW will place the control circuit ready for operation. As the liquid level in the tank drops to the lower limit LL as shown in figure (A). The float switch* contact FS (1-2) will close, see figure (B). Contactor M1 (A-B) is energize by the current that flows from the line L1, toggle switch SW, float switch FS (1-2), contact M2 (11-12), contact R (11-12), contactor M1 (A-B) and to line L2. contact M1 (13-14) will close to maintain con...

Now here’s a digital lock unlike any other, as  it has only two buttons instead of the usual  numeric keypad. The way it works is as simple  as its keypad. Button S1 is used to enter the  digits of the secret code in a pulsed fashion-i.e. the number of times you press the but-ton is determined by the digit to be entered.  A dial telephone uses the same type of coding (now maybe there’s an idea?). Press four  times for a 4, nine times for a 9, etc. Pressing button S2 indicates the end of a digit.    Project Image :    Two-button Digital Lock Project Image   For example, to enter the code 4105, press  S1 four times, then press S2, then S1 once, S2  once, then without pressing S1 at all, press S2  again, then finally S1 five times and S2 once  to finish. If the code is correct, the green LED D1 lights for 2 seconds and the relay is energised for 2 seconds. If the code is wrong, the  red LED D2 lights for 2 seconds, and the relay  is not energised. To change the code, fit a jumper to...

You can make a Toggle Touch Switch with Two Inverter Gates , two resistors, and two capacitors. The schematic diagram of the circuit is shown in the figure below. At power up, the output (of U1A) will be high, and the inverting output will be low because U1A gate will be triggered to ground level by C2. After triggered, the low level of U1A input is maintained by U1B output via R2. If we touch the pad at this condition, where the output is high, then the U1A input will go high because we “short” the voltage of C1 to the input pin, and the low level previously caused by low level of U1B output voltage connected via R2 can’t be maintained because our skin resistance is much lower than 10M. After U1A input goes high then U1A output will go low, and now U1B will go high to maintain high voltage level of U1A via R2, so we can release our finger without loosing the last state. Touching the pad again after we release our previous touching will toggle the output as the condition is reversed. A...