loveuc

Hero999, I am sorry I was quite busy in past couple of days, so could not respond you. I liked the changes you made in the PIC12F683 board circuit. The piezo that I used requires square waves to create sound and the series resistor is unnecessary. The decoupling capacitor is a good practice, I forgot that. The input to LM7805 should be 7-12V, that was my mistake. You are welcome to post the revised version of the circuit and I appreciate for doing this. About my data logger project, I am going to test few things with it this weekend and will ask the administrator to update on website, if required. At last, I also agree with the fact that peer review is important for a good design, but this advertisement asks us to submit the projects that we have already designed and built. Some of them may have some design issues because not all of them were designed by professionals. The three projects I submitted were lying somewhere at the corner of my room for a while. I thought, in this recession, if I can make some extra money by selling them here, then why not, I would buy few more components for my future projects. That was my motivation. And let me tell you one more thing, a good quality, error free, peer reviewed, and purposed to sell project would worth more than $80, and you know that. Thanks, Raj (I hope you didn't mind calling you Hero999 as that's the only name I know of you)

The names in the subject line are two of my projects that are posted in the projects section. I was asked by the Administrator to confirm the polarity of 10uF, 50V capacitor in both the projects. It is connected correctly. The capacitor is found in the TTL to RS232 level translation section in the circuit diagram. If anyone else is confused too, please find the explanation here. http://www.electronics-lab.com/forum/index.php?topic=20610.msg93851#msg93851 Thanks, Raj

I am seeing few people commenting on the polarity of two capacitors that are used in two of my projects posted here, namely Learning board for PIC12F683 and Single chip temperature logger. Both are 10uF, 50V capacitors and are used in TTL to RS232 Level shifting sections of my projects. It seems like they are connected upside down, but that's not true. In order to translate TTL logic '1' (which is 5V) to RS232 logic '1' (which is -3 to -12V), I need negative voltage supply. Since I don't have one on my board, I am stealing it from the TX pin of PC RS232 port. At idle condition (when PC is not transmitting), the TX pin is at logic '1', i.e., at -3 to -12V. I am taking that negative voltage and feeding it back to its RX pin through a 4.7K resistor. So the +ive terminal of the capacitor is grounded, and the -ive terminal is connected to negative voltage supply, which is a proper way to connect a capacitor. The pictures attached here describe how this works exactly. And, when the PC is transmitting, the reverse biased diode connected between the TX and -ive terminal of the capacitance protect it from charging in opposite direction. I didn't mention all these details in the project because I thought it would be too much to put on a hobbyist corner. I hope this answered why the capacitance is connected the way it is. Thanks. Raj