trigger

I still can't figure out how an LED and LDR can measure the heartbeat................. by what theory it is based on?? Anyone can explain this? ??? ???

It is normal for which this circuit is a low power RF transmitter circuit. As Ante said, RF amplifier is needed and need to care about the transmitter power. Also you can do something on the reciever part. A mosfet stage can help to increase the range .

no, high frequency do not mean high bandwidth. It depends on the modulation, the coding , the filtering and the processing power on both transmitter and receiver (in case of digital communication). I prefer high bandwidth more than high frequency.

wavelength and the media reflection/refraction ratio.

Also some microphone frequency response will be poor at low frequency. OT:.... better not to use all capital letters..... that just like shouting and rude....

I think your meter got some problem.... My 12V DC fan (used inside a PC) will run pretty fast and dangerous (I cut my finger once with it......... :P ) with its input voltage at around 12V.

oh.... if the Pb solder and Pb-free solder will mess up, the most problem would be happened to supporting engineers/technicians......... Shops now still selling Pb solder... at least for me, I still got 2 big roll at home........ >:(

You can use dip switch ( in this case 4 channels) at the input ports with resistors as current protection.

I think it is not that easy to build in just using bandpass filters. And the sound frequency generated by the vehicles are not always the same and you have to take care of the "sound" generated by other sources, these are the most critical points! May be you have to analyze the sound frequency spectrum in realtime and look for some peaks..... but will that be working..... I don't know.

I think this one: IZArc is a free software to decompress files. Follow this link: http://www.izsoft.dir.bg/download_izarc.htm

FM wave will reflect by ground...... why not? ??? And the destructive interference is mainly caused by the delayed reflected wave (multipath) + original wave received by the receiver. (for example, in some area, TV set will get some "ghost image" due to the delayed signal mixed with the original signal) I think this book Principle of Mobile Communication by Gordon L. Stüber is a very good reference. It has mentioned some RF propagation modelling (like OKUMURA-HATA AND CCIR MODELS), where can provide you more deeper understanding in RF propagation.

What I know is, the soldering temperature need to be higher (or time longer) and this may bring problems to some components with poor thermal resistant.

Just give you some hints: 1. Try to make use of the ohm's law. 2. Do not calculate the total current in only one equation. 3. Try to divide the whole cirucit in parts and calculate their voltages and currents. 4. Note that at R6, the voltage across it is the same as the battery voltage. Other parts will be more or less the same. 5. Total current = current flow to R6 + current flow to R1 (and the branches) (try to name all node with voltages and currents so that will let you easily get the answer)

rasOfir, You have to try especially you build by yourself. I think no one can guarantee the quality..... If you require high quality sound.... then.... don't put too much expectations.

1. I am not sure what you are mentioning about. But those adaptors are mostly switching mode power supply with low current ouput. 2. cylindrical part on the wires are ferrite which used to shield the high frequency noise that may affect the digital data transfer .

FM transmitter is a bit complicated, you will face a lot engineering issues esp. you do not have any RF equipments.... It is not just soldering...... but a lot tuning and testing.....

It is very strange that you can build the hardware without a software consideration....... :o No one can able to help for no circuits, no general info........ And no one can help if you don't give any try on your own coding!

google already give you the answer............. Edit: attached 2SA933.pdf

It is a good idea...... at least, a clear subject title can save us some times in click into those we interested. And be honest, some of these posts are just homework.... sure we won't like to work these out for others studys.

Alun, I don't have much frequency drift for my 453MHz LC transmitter with voltage variation...... I found that if I use normal variable capacitor to the LC tank, it will drift about 2 to 4 MHz..... but when I use a trim capacitor (I think with better accuracy and temperature variation ) the transmitter frequency is just fine with just 500KHz drift.... even my hands get close to it... it still works within my expected frequency range.

What I mean is, how to measure the power received by the receiver? A standard receiver?? A spectrum analyzer? The RSSI output of the receiver (if it does have)? Receiver audio output (it won't work I thnk)??? Also... is the receiver got a reference antenna? More is, how to measure the transmitter power??

It is hard to comment without the mechanism of the frame and the panel worked by the carpenter. ::)

hmm.......... how do you measure the path loss with the receiver?? just wonder what method you are using........

Use directional antenna..... you can improve the distance by 30 to 50%

I got a mobo with electrolytic capacitor dried out...... It can boot up after a few try but will crash in a second.......