Eventually he's supplied a little more information (in a PM, but I thought I'd post a reply here).

He's wanting to build a cellphone 'jammer', and wants a varying voltage (either random or sawtooth) from 0-23V - presumably for tuning on a varicap diode in an oscillator circuit?. It's also for the course he's on, so doing his work for him seems rather like cheating?, but a few suitable hints should set him on the way.

This bears no resemblance at all to any of his previous questions, which is why we weren't getting any where!.

Anyway, here's one simple solution to the problem:

Use a constant current source from a 24V (or so) power supply to charge a capacitor, the top end of the capacitor is the tuning voltage for the varicap.

Place an NPN transistor across the capacitor, collector to the top, and emitter to ground.

Feed the base of the transistor from a squarewave oscillator, a 555 would be suitable.

When the base of the transistor goes high it turns ON, discharging the capacitor, when it goes high the transistors turns OFF - allowing the capacitor to charge in a linear, giving a nice sawtooth ramp.

The constant current, capacitor value, frequency and mark space ratio of the oscillator, will all require calculating (or finding by experiment).

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PIC programmer software, and PIC Tutorials at:
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what u think this will work

:?:

Attached Images

cir_msr013.jpg (5.6 KB, 275 views)

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plz help friend,s

 

No!.

Here's the relevent part of the circuit I just described!. T1 is the constant current generator.

Attached Images

ramp_generator.gif (3.1 KB, 272 views)

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

if will be great ful if u give me value,s of circuits R? C? and all other,s

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plz help friend,s

 

'YOU' need to work them out, based on your particular design choices, the operation of the circuit is pretty obvious - we're not here to do your assignments for you, although we don't mind offering suggestions :lol:

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

but what is wrong in idea plesae just post you idea froom where to begin

as u know my square wave circuit :!:

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plz help friend,s

 

Nigel I say he has had enough hints. If he is in an electronics class and is this far in. He should be able to do the mathematical equations to figure this out and he should be able to figure out what is wrong with his idea himself. Personally I'm beginning to think he is just trying to get us to do most of the work for him. No offense but thats what it seems like to me.