IC Polarity and Electrical Kit Questions - Page 1
Forum section: electronics / beginners

author: JeepRadioGuy
author_rank: Newbie
timestamp: April 12, 2015, 08:18:57 pm
content: Hi Everyone,I am a newbie and am assembling a my first electronics kit since my childhood. This time it has an integrated circuit and the vague instructions warn that me to " watch the polarity" of the chip before installing it. I have attached the schematic, along with pictures of the PCB and the IC Chip.Question: How do I determine the polarity of either the chip, the circuit schematic, or the circuit board.Perhaps stated another way: Where is pin 1 on the chip?Question A: What is U stand for ? As in U1 and U2 - that looks like the IC Chip holders.Question B: What is the correct installation for U1 & U2? ----- I see the semi circular cutout depicted on the PC board as well as the components U1 & U2 therefore it appears as thought those are directional, even though these "U" components appear to be identical in either direction.Question C: What is the correct installation for IC1 and IC2?Looking at the Datasheet for the LM324 IC athttp://www.engineersgarage.com/electronic-components/lm324n-datasheetit appears as thought the semi-circular depression in the chip pictured would be the top of the chip, therefore pin 1 would be on the left... Just a guess on my part.Looking at the schematic and the board I see that Pin 1 (IC Operational Amplifier 1) on U1 connects to R3 so I think I know where pin one goes... Similarly I see that on U2 the Pin 1 appears to go to R11 However on the PC Board it looks as though Pin2 goes to R11 which mystifies me.Question D: Why are there multiple datasheets for these chips when they appear to be the same?I tried to look up the datasheet and found a bunch listed at:http://www.alldatasheet.com/view.jspAt the TI website I found yet a different set of parameters that may or may not equate to these datasheets.http://www.ti.com/product/lm324Any help you could give would be greatly appreciated.Thank you.Jim(JeepRadioGuy)

author: Laura
author_rank: Contributor
timestamp: April 12, 2015, 08:42:42 pm
content: "U" is a common circuit diagram component prefix meaning "integrated circuit".Pin 1 on an IC is indicated by a little dot. This is clearly visible on your LM324's. Sometimes the end with pin 1 has a notch of some sort instead. Your circuit board and your sockets are marked this way. Sometimes both methods are used.Sometimes circuit boards have a square pad for pin 1 and round pads for all other pins. This way you can identify the orientation even without a silk screened label.Pin 1 on U1 will be closest to the "U1" marking. Pin 1 on U2 will be by the gap between R8 and R10. Also, the silk screened writing on the board and the text on the LM324's will all be oriented the same way.The schematic doesn't match the circuit board! That's why you're having some confusion about pin 1.

author: Simon
author_rank: Unknown
timestamp: April 12, 2015, 08:44:44 pm
content: match up all of the semi circular depressions on the end of the symbol, the socket and the chip and you should be ok.

author: JeepRadioGuy
author_rank: Newbie
timestamp: April 12, 2015, 10:11:55 pm
content: Laura, Simon,Thank you for the great info... This really helps.Best wishes,Jim