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David Cook ROBOT ROOM™ |
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ROBOT ROOM FEEDBACK
Photoresistors:
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From: Kevin Morrison Sent: Friday, February 22, 2002 12:33 PM Subject: Photoresistors Hello, I am currently reading your book and building my first robot. I am having a lot of trouble getting a true value of resistance for the photoresistors. Because these little guys are responsible for the guidance, I am convinced that this measurement is extremely important and need an acurate number in order to pair the resistors. It seems every time I test, there is a new result. What am I doing wrong or what can I do to give more acurate numbers? Sincerely, Truelyunabletoreadresistance |
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David replies: Hello Kevin, Yes, measurements of photoresistors will vary considerably based on ambient (room) lighting and temperature. But, even weirder is that the value may not settle in one place, even if you wait a while. Don't sweat it. Your primary goal in testing the photoresistors is to knock out any defective ones. These will not change value or will have really low or really high values -- especially compared to the rest of the lot. Your secondary goal is to roughly match the photoresistors. Stick one up to a light bulb, count to 5, record the value. Stick it under a dark desk, count to 5, record the value. Good enough. Because of the balancing potentiometer (R1) and the striking contrast of the line on the floor, the photoresistors don't have to be matched exactly. Truth be told, the four photoresistors for Sandwich were picked at random from a previously defective-removed lot. And Sandwich performs beautifully. The subsequent Sandwich brothers had more carefully matched values, but show no differences in performance. Hope this helps, David |
Surface-Mounted Devices:
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From: Mario Becroft Sent: Thursday, August 03, 2000 12:13 AM Subject: As to whether I have SMD equipment in my basement ;-)... In fact I just hand solder the components with an ordinary soldering iron. When you get used to it they are actually easier to solder than leaded components. And some of my boards would be about 5x the size if I used through-hole components (supposing that all of the components were available in through-hole versions...) |
Soldering tips from Mario appear on the PCB page.
Color Choices:
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From: Tom Gavin Sent: Tuesday, August 22, 2000 6:06 PM Subject: Colors The green links [now yellow] are a bit "fluorescent" on my iMac. Readable, but maybe you could darken them a bit. Pukey and bloody are how I would describe your colors. |
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David Cook ROBOT ROOM™ |
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