Isolating bridge rectifier

I want to use the short audio output from my iPad to generate a brief 5V pu lse for an Arduino circuit. I am using an existing pre-amp to take the roug hly 200mv pk-pk ac to about 8V pk-pk. I thought I?d follow that wit h a simple 4-diode bridge rectifier. The pre-amp and the Arduino circuit ha ve a common ground rail. So is the correct method to take each of the pre-a mp outputs to the bridge via a capacitor? Using 0.1uF, this appears to work OK (with a 4.7V zener to keep the pulse under 5V). But it does look a bit strange, so I?m wondering if there?s a neater way please?

Terry

Reply to
terrypingm
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How about a 2-diode voltage doubler? Load that with the zener and a discharge resistor.

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John Larkin         Highland Technology, Inc 

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Reply to
jlarkin

pulse for an Arduino circuit. I am using an existing pre-amp to take the ro ughly 200mv pk-pk ac to about 8V pk-pk. I thought I?d follow that w ith a simple 4-diode bridge rectifier. The pre-amp and the Arduino circuit have a common ground rail. So is the correct method to take each of the pre

-amp outputs to the bridge via a capacitor? Using 0.1uF, this appears to wo rk OK (with a 4.7V zener to keep the pulse under 5V). But it does look a bi t strange, so I?m wondering if there?s a neater way please?

You should be fine using just one half of the AC signal (after the pre-amp) . A single diode feeding a cap. Add a bleeder resistor across the cap for the end of the pulse. And a series resistor into the zener so it won't ge t hot (you can use the zener directly if the pulse is short enough). I dre w it in LTSpice:

Version 4 SHEET 1 904 680 WIRE 608 48 576 48 WIRE 704 48 608 48 WIRE 848 48 784 48 WIRE 880 48 848 48 WIRE 160 64 112 64 WIRE 336 64 160 64 WIRE 480 64 400 64 WIRE 576 64 576 48 WIRE 576 64 480 64 WIRE 880 96 880 48 WIRE 480 112 480 64 WIRE 576 112 576 64 WIRE 112 128 112 64 WIRE 112 240 112 208 WIRE 480 240 480 176 WIRE 480 240 112 240 WIRE 576 240 576 192 WIRE 576 240 480 240 WIRE 880 240 880 160 WIRE 880 240 576 240 WIRE 112 272 112 240 FLAG 112 272 0 FLAG 848 48 Vout FLAG 160 64 Vin FLAG 608 48 Vcap SYMBOL voltage 112 112 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value SINE(0 8 1k 0 0 0 100) SYMBOL diode 336 80 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D1 SYMBOL cap 464 112 R0 SYMATTR InstName C1

SYMBOL res 560 96 R0 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL res 800 32 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 1k SYMBOL zener 896 160 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D2 SYMATTR Value 1N750 TEXT 288 376 Left 2 !.tran 1

Reply to
sea moss

Thanks both, much appreciate the fast replies. I'll breadboard later this afternoon but the sims look good.

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Digressing: it's probably decades since I used LT Spice rather than my familiar CircuitMaker 2000. Just installed it to run sea moss's version. To save me some reading, from the state shown in my screenshot how would I quickly display say only Vout please?

If I decide to try switching to LTS for the few sims I do as a hobbyist, can anyone narrow down almost one million hits for 'LT Spice tutorials' to a few recommendations that should get me up and running please?

====================

sea moss wrote:

Reply to
Terry Pinnell

Two comments: The input isn't grounded, and the output goes up but doesn't go down.

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John Larkin         Highland Technology, Inc 

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Reply to
jlarkin

Once you run the sim, there is an icon at the top of the screen for "pick v isible traces", you use that to select what you want to look at.

I don't know how much value there is in watching tutorials on circuit simul ators, unless there's a fancy function that is weird to setup. Much better to just poke around, and google things you can't figure out. I will say, on LTSpice, the first time you try to place a voltage source it seems odd. There is an icon of an AND gate for "add component", click on that, and at the far right you will see "voltage".

I prefer Simetrix since I have been using it almost daily for years; I'm fa st at all the basic stuff. But, it's not free, so when I'm home I switch t o LTSpice.

Reply to
sea moss

Thanks, learning by doing is indeed my preferred approach, although it can often accelerated by the right tutorials or books.

Reply to
Terry Pinnell

Thanks, yes, forgot that. Here's the revision:

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As for the indefinite signal output, that's because I'm not sure how to configure the simulation settings in CM 2000 to show the sine abruptly becoming zero amplitude!

I'll have a try at it with LT Spice soon, as sea moss's version did not have that issue. I thought I might fix it by playing with line 3 below, but it didn't see to change anything.

*Spice netlist for Circuit: C:\Users\terry\Dropbox\Electronics\CIRCUITS\MY FINISHED CIRCUITS\Rectifiers\VoltageDoubler-2Diodes.CKT D4 0 R1_1 D1N750 V1 V1_1 0 DC 0 SIN(0 8 1k 0) AC 1 0 D1 V1_1 R1_2 DDIODE D2 0 V1_1 DDIODE C1 0 R1_2 10uF C2 0 0 10uF R1 R1_1 R1_2 1k .SAVE R1_1 R1_2 V1_1 @d4[id] @v1[p] v1#branch @v1[z] @d1[p] @d1[id] @d2[p] .SAVE @d2[id] @c1[p] @c1[i] @c2[p] @c2[i] @r1[p] @r1[i]
  • Selected Circuit Analyses : .OP .TRAN 20u 5m 0 20u

  • Models/Subcircuits Used:

*1N750 4.7V 500mW Si Zener pkg:DIODE0.4 A,K .MODEL D1N750 D(IS=1E-11 RS=9.066 N=1.27 TT=5E-8 CJO=4.351E-10 VJ=0.75
  • M=0.33 BV=4.519 IBV=0.01 )

*DIODE Default diode PARAMeter values pkg:DIODE0.4 A,K .MODEL DDIODE D() .END

Reply to
Terry Pinnell

Try this maybe:

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Use LT Spice! It lets you add delay to a sine start, and specify a number of cycles.

--
John Larkin         Highland Technology, Inc 

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Reply to
jlarkin

====================

That sims fine thanks, after playing with C and R values for a while.

Thanks, the latter feature allowed the output to return to zero, which CM fails to accomplish. The output reached 4.7V V quickly (about 1ms), albeit in two 'steps'.

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I suppose I'll get used to it but LTS's UI seems a bit rough in places. For example, I had to remove redundant component text in my image editor for the screenshot below, as it seems that cannot be done in LTS.

BTW, I was surprised the zener did not need a series resistor.

Reply to
Terry Pinnell

I wouldn't expect a little audio amp to output enough current to fry the zener, but the first cap can be sized to limit the current too. 8 volts p-p doubled into a 5 volt zener, with two diode drops, won't pump a lot of current either.

The caps don't need to be equal.

What diodes did you use? The default in LT seems to be a sort of 1N914 type.

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John Larkin         Highland Technology, Inc 

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Reply to
jlarkin

I used the default and changed later to 1N914, the first entry in the list.

Reply to
terrypingm

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