Square wave to psuedo-sine wave?

Mar 23, 2010 29 Replies

"Phil Allison"

Contrary to what you think, the OP seems like he would be happy with a sine wave with only 1% distortion.

** Fraid that POS has a lot more than 1% THD.

The diodes will rectify RF but at the output the signal level should be several orders of magnitude higher than the RF.

** The OP wants to link his device to a transmitter.

The amount of RF energy is serious.

Did you read his post at all ??

So would not expect that to be a problem.

** Yawnnnnnnnnnnnnnnnnn....

.... Phil

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That is a nicer output, but that also requires a 15mH coil. Wouldn't that be a little big? This will be going into a small payload container with 3" diameter.

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Thanks Don. Truly weird! I plan to code it up and play around with this when time permits. So, the original poster could put this into a single chip PIC and forget about his square wave source. He'd still need to run a D toA to get an analog output, would he not? Within that algorithm he could also pull out a square wave too if needed. Frequency could be anything within the speed of the processor with appropriate, even externally controlled internal delays and of course be crystal controlled and very stable. Hmmm. I already have a use for this. Thanks again. Bob

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They're about the size of 0.4W resistors but if you're stuck for space then it's not an option. I had in mind this ... 'Epcos' part# B82144A2156J000 A pic of a similar item ...

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Hm, what about this one? Looks promising:

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Yep. Fine!. (DigiKey 811-1302-ND for the 15mH)

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How about this: Version 4 SHEET 1 880 680 WIRE 208 0 16 0 WIRE 208 16 208 0 WIRE 16 32 16 0 WIRE 16 128 16 112 WIRE 208 144 208 96 WIRE 336 144 208 144 WIRE 208 160 208 144 WIRE 16 256 16 208 WIRE 208 256 208 224 WIRE 208 256 16 256 WIRE 16 352 16 256 FLAG 16 352 0 SYMBOL ind 192 0 R0 SYMATTR InstName L1 SYMATTR Value .00932 SYMATTR SpiceLine Rser=110 SYMBOL cap 192 160 R0 WINDOW 0 42 38 Left 0 WINDOW 3 26 65 Left 0 SYMATTR InstName C1 SYMATTR Value .68e-6 SYMBOL voltage 16 112 R0 WINDOW 3 24 104 Invisible 0 WINDOW 39 0 0 Left 0 SYMATTR Value PULSE(0 5 0 1e-7 1e-7 250e-6 500e-6) SYMATTR InstName V1 SYMATTR Value2 AC 1 SYMBOL res 0 16 R0 SYMATTR InstName R1 SYMATTR Value 10 TEXT 40 288 Left 0 !.tran .1 TEXT 40 320 Left 0 !;ac oct 256 10 10000 The coil is a Caddell-Burns 6740-61 (6.8 - 12mH) variable inductor: http://www.caddell-burns.com/PDF/A1042.pdf You can use it to tune to 2kHz, dead nuts, but that tunability comes at a price: http://www.caddell-burns.com/priceList/Price_List_Pg_2.pdf and the cap is any garden variety 0.68µF polyester cap. JF

With a 10% of fc range i would use an integrator first then use an=20 active RC bandpass filter.

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How many _well designed_ Wien bridge oscillators have you seen that get=20 hammered by EMI/RFI?

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