Nuts and Volts - April 2014

READER-TO-READER TECHFORUM

>>> QUESTIONS

555 Anomaly

I have found an interesting anomaly with the 555 IC. Everywhere I've read and looked, the #4 (reset) pin has voltage held high to allow the IC to conduct, and then dropped low to turn off (reset) the IC.

I have 8.58V at 39. 5 mA at VCC (#8) pin when the IC conducts. As you can see in the schematic, I am controlling the IC through the reset pin (#4) with a CdS photocell photoresis-tor. When light is removed from the CdS photocell and the IC conducts, it sends 6.5V at 18. 2 mA to the output (#3) pin and LEDs. Apply light to the CdS photocell and the IC stops conducting; you then get -0.2V at 0.0 mA at the output (#3) pin. Since I added a 4. 7 µF electrolytic capacitor to the output pin, the IC now conducts 7V to the LEDs.

I am an electronics hobbyist who has been learning electronics for one year. I welcome any comments and ideas anyone has about what is going on with the IC.

#4141 Robert Calk Jr. via email Arduino Power Requirements I'm using an external 6V supply to power an Arduino circuit which is giving me problems. I heard somewhere that the Arduino requires at least 7 or 8 VDC input. Doesn't the Arduino run on 5V? Can someone clarify? #4142 Arturo Martinez via email

How Much Heat Can A Battery Take?

I need to shrink wrap sets of AA lithium batteries for a radio project. Can I safely heat the shrink wrap with a hot air blower, without harming or causing the batteries to explode?

#4143 James Cook Lansing, MI

Receiver ... Not

I inherited an old tube-type short wave receiver from my grandfather. It produces nothing but static, even after I replaced all of the vacuum tubes. All of the switches are good. Any ideas where to go from here?

#4144 Ben Hill

Norfolk,VA

Self-Dimming Light Switch

Can you give me the schematic for a light switch that automatically dims the lights between, say, 10 pm and 6 am? I want something in between total darkness and blazing brightness for raiding the kitchen refrigerator in the middle of the night. #4145 Alfonzo Garcia

Little Rock, AR

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