Mwee Posted February 14, 2006 Report Share Posted February 14, 2006 Could someone tell me if this circuit would work, and also, if the 22M pot is needed? would a smaller one work - 22M pots are.. impossible to find. (see attachment) Quote Link to comment Share on other sites More sharing options...
prateeksikka Posted February 14, 2006 Report Share Posted February 14, 2006 hi Mweei cant see the circuit u have posted properly here clearly.the image is blurred....yeah u can do with a smaller pot always but the only thing is the fear of getting damaged .because it will although divide the voltage but it wont offer much resistance between terminals 1 and 3.thats it otherwise u may use an auto transformer.good luck Quote Link to comment Share on other sites More sharing options...
ante Posted February 14, 2006 Report Share Posted February 14, 2006 Hi prateek,There is nothing wrong with the picture, it’s perfectly clear!Is it blurred…… what have you been drinking? ;D Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 14, 2006 Report Share Posted February 14, 2006 The schematic was a HUGE fuzzy JPG. I shrunk it and posted it as a clear PNG but had to start with the fuzz. It should look better on this page.The 22M pot is backwards and if set to max, the bias current of the LM3914 across it would show a reading of half-scale or more without a signal. A 1M pot would work fine.I removed a resistor that didn't do anything and added a very important supply bypass capacitor that all IC circuits need, especially if they use a battery.The remaining resistor sets a fairly low LED current of only 5mA. A 560 ohm resistor would make the LEDs much brighter. Quote Link to comment Share on other sites More sharing options...
indulis Posted February 14, 2006 Report Share Posted February 14, 2006 You have to be careful with LED's nowadays..... the old rule of thumb doesn't apply across the board anymore. For example, the TLLG/R/Y540 LED from Vishay is spec'ed with a current of 2mA and has a max forward current of 7mA. Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 14, 2006 Report Share Posted February 14, 2006 The Vishay low-current LED is very dim by today's standards. Any fairly modern LED would be brighter and have a wider angle at its low current. At 20mA, a modern LED would be much brighter. Quote Link to comment Share on other sites More sharing options...
indulis Posted February 15, 2006 Report Share Posted February 15, 2006 I do believe you have that backwards............ LED's (traditional colors) in "modern" times have seen a reduction in current, not the other way around. Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 15, 2006 Report Share Posted February 15, 2006 Hi Indulis,I haven't seen an LED that performs as poorly as the Vishay TLLR5401 for many years.The Fairchild MV8141 red LED that I use is 10 times brighter, has a wider viewing angle and can be 57 times brighter at its max continuous current. They are both diffused and the Fairchild LED costs only 5 cents more. Quote Link to comment Share on other sites More sharing options...
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