source2 Posted June 19, 2005 Report Share Posted June 19, 2005 At first I want to know it is possible to build. (cheap, I havent got a lot of money)I want to make frequency between 10 HZ and 30 Hz. (With Ne555 IC and a potmeter, because it is cheap) It necessary for the VCR head I want to change the frequentely with the potmeter? CAn somebody give me a schematic ?THX Quote Link to comment Share on other sites More sharing options...
hamoodyjamal Posted June 20, 2005 Report Share Posted June 20, 2005 Hi, I’m no expert, but I think it would be quite difficult to use a POT to change the frequency of such small range. I have used the 555 timer for some time and am quite familiar with it. I have a schematic which I took of the Maplin catalogue which has worked quite nicely with me. I’ve digitized it. Have a look.Regarding the timing capacitor and resistors, I have calculated possible values to oscillate 20HzRa = 220K Ohm + 100K Ohm Pot in series (the pot should be set to about 80K Ohm).Rb = 220K OhmC = 0.1uFRL = Resistor in series with the load. 100 Ohm would be OK for an LED. There is also a decoupling capacitor which can be attached in parallel with the power supply. 47uF 16V would be OK.Along with the schematic came a formula to calculate the frequencyf = 1.44/[(Ra +2Rb)xC]Resistance in Ohm and Capacitance in Farad.To simply things so that you can use C (capacitance) in Micro Farad (uF):f = 1440000/[(Ra +2Rb)xC]Remember 1000000uF = 1FFind the schematic attached. All the components are very cheap. Most likely the 555 timer would be the most expensive part.Also remember that the resistors and capacitor have tolerance of about 10%. That’s why it’s a good practice to use a POT in oscillator circuits.You can try and tune the POT for different frequencies.Hope this helps. There are also many other circuits on the web. Bye! Quote Link to comment Share on other sites More sharing options...
audioguru Posted June 20, 2005 Report Share Posted June 20, 2005 Hi,I had good success by using an LM331 V to F generator, a multi-turn cermet trimpot and a regulated supply. It operates at a higher frequency with a stable metalized-plastic timing capacitor so my frequency counter can measure its frequency quickly and accurately. Its output frequency is divided down with a digital divider and is very stable. It uses a Johnson counter to make an over-sampled stepped sine-wave and a switched-capacitor lowpass filter IC to make perfect sine waves. ;D Quote Link to comment Share on other sites More sharing options...
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