Circuit Lake

Daniel designs this Metronome with a few simple electronic components.The Metronome is any device that produces a regulated audible and/or visual pulse, usually used to establish a steady beat, or tempo, measured in beats-per-minute (BPM) for the performance of musical compositions. It is an invaluable practice tool for musicians that goes back hundreds of years.

Material Needed:

1. 555 IC
2. 3x 1K Ohm Resistor
3. 2x 22uF 16V Capacitor
4. 9V Battery
5. 8 Ohms Speaker
6. 250K Ohms Potentiometer

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When you need connect your Microcontroller Project to COM port in PC you need RS 232 converter. There are many chip to solve the problem like MAX232, DS275 etc. But if you need simple and chep for RS 232 converter, i though this circuit will be usefull for you. The design made by Wichit Sirichote.

“A circuit diagram shown above was used two small signal transistor, NPN and PNP transistors. Dash line separate transmitter and receiver circuit. For those who need only transmitter circuit can use above circuit (and GND (5) signal ). Technically the RS232C is -3V to -12V for logic ‘1′ and +3V to +12V for logic ‘0′. The transmitter circuit uses PNP transistor, BC557. While in mark state the TxD signal is logic ‘1′, Q1 turns off. TxD (pin3) then provides -9V (depends on what converter chip being used for COM1, say) to RxD (pin2). For space state, TxD control signal then becomes logic ‘0′, which turns on Q1, the approx. +5V is then fed to RxD (pin2). With this method, while sending data has being made, TxD (pin3) must stable at -9V, say”

There also some modification from above circuit. For more detail you can download here.

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Evil Mad Scientists have create cool and simple Darkness Sensing LED ever. It’s only need few component: a CR2032 lithium coin cell (3 V). LED, an LTR-4206E phototransistor, a 2N3904 transistor, and a 1 k resistor. You can choose it for your first project during learning electronic.

“When light falls on the phototransistor, it begins to conduct up to about 1.5 mA, which pulls down the voltage at the lower side of the resistor by 1.5 V, turning off the transistor, which turns off the LED. When it’s dark, the transistor is able to conduct about 15 mA through the LED. So, the circuit uses only about 1/10 as much current while the LED is off. One thing to note about this circuit: We’re using a red LED. That’s because the voltage drop across the transistor allows less than the full 3 V across the LED. The full three volts is really only marginal for driving blue LEDs anyway, so two-point-something really doesn’t cut it.”

by Alan Winstanley

De-soldering is required when electronic components need to be removed from a circuit, usually because they are faulty. It may sometimes be necessary during testing or assembly, if a wrong part has been fitted or a modification has to be made. In the field, it’s not uncommon for faulty electronic components to be swapped out, or poor joints (perhaps “dry” or gray joints) to need re-making properly, months or years after manufacture. Experienced engineers can often diagnose a particular faulty joint immediately, because they may have seen the same problem on similar electronic equipment before, especially if the equipment has a “reputation”. A proper desoldering technique can soon be acquired with practice - all you need to do is buy some scrap boards to have a go with, and desolder to your heart’s content!

The next photo sequence illustrates the basic steps for desoldering a printed circuit board, in order to remove a faulty part. Both the technique for using a desoldering suction pump as well as desolder braid are illustrated.

Remember - Practice makes perfect.

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(1) The two solder joints to be desoldered, to enable a faulty electrolytic capacitor to be removed from the printed circuit board.	(2) If using a suction-type desoldering pump, apply the soldering iron tip first to melt the solder joint (say for 1-2 seconds). Ensure the spring-loaded desoldering pump is ‘primed’ and ready to go…
(3) The PTFE nozzle of the desoldering pump is applied to the molten solder and the spring-loaded plunger is then immediately released, drawing the molten solder up into the pump. Remove the soldering iron tip. Repeat the process if needed. Handy tip: sometimes it helps to add some fresh solder and then desolder the whole joint.	(4) The first p.c.b. joint, now desoldered. The second joint will be desoldered using traditional desoldering braid.
(5) Select a suitable width of desoldering braid, and press it down onto the COLD joint using the hot tip of the iron. A flat soldering iron bit is preferable.	(6) The molten solder is drawn up by capillary action into the desoldering braid. Take care not to overheat the board (the p.c.b. copper track may lift off), nor ‘drag whiskers’ of solder over the board, nor let the braid solidify onto the joint! Remove the braid while the joint is still molten.
(7) The faulty electrolytic capacitor dropped out of the board after desoldering. Sometimes, it may need persuading with pliers…. but don’t overdo this or you risk damaging the copper tracks on the PCB.	(8) Close-up photograph of both joints, now desoldered and ready for the replacement component to be fitted.

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