Forums

Dual Offest Sub-audio Test Signal

Started by Unknown May 23, 2014
On Sat, 24 May 2014 11:21:01 +0100, piglet <erichpwagner@hotmail.com>
wrote:


>Same current will do. The voltage sign will depend on which way round >you attach the scope probe and ground clip.
Sure but I am mean to keep either the probe or ground clip stationary on one terminal while measuring the other ends of the coils. That will show the relative waveforms.
>And you want the current maxima to occur at the same time in both coils >or in other words be in-phase. So it looks very like just wiring the two >coils in series will do what you want? >
You mentioned this before. But I am unable to visualize how one coil can swing positive while the other swings negative in a series connection. Can you draw me a word picture? John Gillmore
On Sat, 24 May 2014 12:05:30 +0100, piglet <erichpwagner@hotmail.com>
wrote:


>Looking at the waveforms you posted at the start I do see that when one >coil has 1V across it you want the other to have 4V across it. In other >words the currents are in anti-phase. >
When one coil is 4V isn't the other at -1V? The phase is the same. Only the offset differs. That's what I see. http://www.4shared.com/download/Z_6zeE2yce/dual_dc_offset.jpg?lgfp=3000 John Gillmore
On Sat, 24 May 2014 22:25:30 +1000, "Phil Allison" <phil_a@tpg.com.au>
wrote:


>** But is full of horrible errors - too many to fix by mere NG posts. >
Gee. This is discouraging. How about putting on your "nice guy" hat Phil and listing maybe three of these horrible errors? Just to get me started on the road to recovery. In the revised circuit below, I have already corrected the horrible diode reversal that piglet pointed out, and added an offset pot for the signal input from the function generator. http://www.4shared.com/download/jKjCKu1aba/dual_current_driver_3.jpg?lgfp=3000 Also, if the coils are not in phase as shown, how can they be rewired so they are? Thanks again, if you please. John Gillmore
In article <8puvn9leks6kp7g3j9et6s9jnp24eda17l@4ax.com>, 
jgillmore@netscan.com says...
> > Can someone please help with this project. I am unable to find > anything similar in the form of an existing design. > > The objective is to apply a 10Hz test signal, generated with a lab > function generator, to two air core solenoids of 50R. > > OK, here is the different part. > > One solenoid must be fed with a positive offset signal, and the second > with an identical negative offset signal. > > Given a 12VDC supply, each signal would be 4Vpp, offset 1V, one above > and one below DC. > > This diagram shows it in detail: > > http://www.4shared.com/download/Z_6zeE2yce/dual_dc_offset.jpg?lgfp=3000 > > I am guessing this can be done with a BD139/BD140 pair or similar > running off a split 12V supply with a virtual ground. > > However, I am uncertain how to configure the supply so as to offset > each rail from ground to achieve the desired effect. > > Or perhaps there is another approach. Any advice would be very much > appreciated. > > John Gillmore
there is a simpler approach to your problem.. 6V+ +--------+ + | .-. | R1 | | | | | | R2 '-' + 6V Pk-Pk ___ | |/ +-------+|___|-------+----+| 2N2222 type + |> / \ + ( ~ ) | \_/ | | + GND C| C|50DCR C| | | === GND (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de) Calculate R1 and R2 so when the generator is at 0 volts the emitter output is at the center point of the sine. Adjust generator output so that you'll never put the output in the off state, or add another R at the base to common to prevent the generator from over driving it into the off state, which means you'll need to decrease the value of R1 of course to correct for that. As for the other coil, use the same circuit but pass the generator through an inverter stage or use a PNP equal circuit. Jamie
On Friday, May 23, 2014 7:12:27 PM UTC-7, jgil...@netscan.com wrote:

> The objective is to apply a 10Hz test signal, generated with a lab > function generator, to two air core solenoids of 50R.
Usually a solenoid is an inductor, and '50R' indicates a resistance instead. Is this a nominal 50 ohm inductor (which would usually be measured at 1 kHz) as in a speaker? Or, is it a resistance of the wire windings?
> One solenoid must be fed with a positive offset signal, and the second > with an identical negative offset signal.
But each solenoid has TWO terminals; which is driven, and what is done with the other? Are some terminals grounded? To be clear: the diagram indicates two voltage waveforms, and there are four terminals in the system.
On Sat, 24 May 2014 19:39:20 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:


>Usually a solenoid is an inductor, and '50R' indicates a resistance instead. >Is this a nominal 50 ohm inductor (which would usually be measured >at 1 kHz) as in a speaker? Or, is it a resistance of the wire windings? >
I assume 10Hz is near enough to DC so 50R of wire would be 50R impedance.
>> One solenoid must be fed with a positive offset signal, and the second >> with an identical negative offset signal. > > But each solenoid has TWO terminals; which is driven, and what >is done with the other? Are some terminals grounded? >To be clear: the diagram indicates two voltage waveforms, and >there are four terminals in the system. >
Please see this diagram. http://www.4shared.com/download/jKjCKu1aba/dual_current_driver_3.jpg?lgfp=3000 Thanks for your reply. John Galimore
On Saturday, May 24, 2014 8:36:38 PM UTC-7, jgil...@netscan.com wrote:
> On Sat, 24 May 2014 19:39:20 -0700 (PDT), whit3rd <whit3rd@gmail.com> > > wrote:
> > But each solenoid has TWO terminals; which is driven, and what > >is done with the other? Are some terminals grounded?
> Please see this diagram.
> > http://www.4shared.com/download/jKjCKu1aba/dual_current_driver_3.jpg?lgfp=3000 >
The diagram indicates a 'synthetic ground' buffered by an op amp, which is never used. You would do better to run the 220k pullup/pulldown directly to one terminal of the AC source, and use the op amp to buffer the other terminal into the junction of D1 and D2. Then Q1 and R8 get replaced with a 1.5k ohm pulldown. There are power op amps (L272 perhaps?) that can simplify this; I'm uncertain of the use of 1N4002 diodes in biasing (those D1/D2 diodes should be matched to the drive transistors, and 1N4002 is kinda ... generic). How's this? <http://www.digikey.com/schemeit/#u7g> I'm still not sure what's the goal... The given input AC amplitude will saturate your amplifiers; perhaps the AC source can be attenuated? I'm also unclear on the function of D3 ... D6, which seem to waste energy. should be adjusted downward?
On Sat, 24 May 2014 12:12:27 +1000, jgillmore@netscan.com wrote:

> >Can someone please help with this project. I am unable to find >anything similar in the form of an existing design. > >The objective is to apply a 10Hz test signal, generated with a lab >function generator, to two air core solenoids of 50R. > >OK, here is the different part. > >One solenoid must be fed with a positive offset signal, and the second >with an identical negative offset signal. > >Given a 12VDC supply, each signal would be 4Vpp, offset 1V, one above >and one below DC. > >This diagram shows it in detail: > >http://www.4shared.com/download/Z_6zeE2yce/dual_dc_offset.jpg?lgfp=3000 > >I am guessing this can be done with a BD139/BD140 pair or similar >running off a split 12V supply with a virtual ground. > >However, I am uncertain how to configure the supply so as to offset >each rail from ground to achieve the desired effect. > >Or perhaps there is another approach. Any advice would be very much >appreciated. > >John Gillmore
--- I'm late into the fray. Is your supply's output: +6V 0V -6V or is it lacking a common? John Fields
On Saturday, 24 May 2014 03:12:27 UTC+1, jgil...@netscan.com  wrote:
> Can someone please help with this project. I am unable to find
Dear John, Please have a look at the two sketches in the attached link https://dl.dropboxusercontent.com/u/16764432/SED_JG_MAY14.pdf they should help you get going. piglet
On Sunday, 25 May 2014 10:33:44 UTC+1, piglet  wrote:
> Dear John,
Ooops...I meant John Gallimore the OP, not John Fields.