Voltage follower with a step function (need a design for one)

Thanks for the reply. So is your "do not snip" directed at everyone or someone specific? I have no idea what prompted this threat of yours.

Rocky

I don't know anything about you in particular, but SED is loaded with parasitic leeches who love to insult or otherwise provoke people indirectly by doing that kind of thing, and at the same time, these parasitic leeches will maintain huge quotes in off topic threads comprised of pure babble.

Calm down Fred.

Yabut ... Fred posts great stuff. Wouldn't it be nice if, at least once in a while, the op's answer was: "Wow! Thanks a lot ..." or "Geez - your circuit works great..." or "Thanks for the help! Could you explain ...?" or something like that?

Ed

What on earth are you talking about Fred? I am at a loss so see how I

1. responded impolitely to you, or
2. insulted you, or
3. provoked you.

if you are going to make such threats and liken my actions to those done by a parasitic leech, the least you could do is make yourself clear about what exactly the problem is. Please refer to the EXACT post of mine which offended you and tell me WHY. Only then can I see how I may have done something wrong in your eyes.

Rocky

Huh? As the original poster , my first response to Fred was to ask him how the circuit worked because I didn't immediately see it. There's no way I'm about to sing the praises of something I don't understand. So then Fred goes on to explain his circuit, and in the same breath insults me for goodness knows what.... So I reply by saying thanks (for the explanation) and also asking how I had offended him. Is that still a problem for you Ed?

Rocky

Thanks John, this was indeed the problem, I changed the extension to .asc and it ran fine. So now I have had a chance to simulate both the circuits, and I too can see what you mean. The Vce_sat is definitely lower when the collector is grounded rather than the emitter. I got identical voltages to those listed by Jonathan Kirwan above. I'm not used to working with transistors designed as switches, I've really only used them as signal amplifiers. Even though this thread is now getting rather off the OT (because such a small difference in saturation voltage will not confer a noticeable advantage to the main circuit ) , I still don't understand what Ken Smith meant when he said "If the max signal voltage is under about 7V, swap Q1's E and C legs." I tested the circuit with Vin=12V and the cct. with the collector grounded still had a lower Vce_sat. pm me if you want a copy of either cct or screen shot of the sim.

regards Rocky

"Is that still a problem for you Ed?"

Hi Rocky,

The above would set some people off. Me - I don't care. But just so you know, I don't have a problem, and did not have a problem. And I have no interest in who insulted/did not insult or whatever the heck is or is not going on with regards to insults.

My post to Win actually had nothing to do with what you posted. I just shake my head in wonder at the ratio of *excellent* answers from Fred to the number of replies that express appreciation. Fred's phrase "parasitic leeches" - having nothing to do with you - may be a perfect description of those who post, get great replies, and never say a word. I'll add that this happens to others besides Fred.

Ed

I'm not sure if anyone has asked this - Why? What is your objective.

A more creative response can be gained from an objective question.

-Andrew M

Thanks Ed. I am still racking my brains to figure out what Fred thinks I actually did wrong in his eyes. It may be blinking obvious to you and others reading this thread - but if you know (i.e. when you say "The above would set some people off" what do you mean), could you spell it out for me? Sorry if I'm being persistent or trivial here, but Fred hasn't replied back to tell me what I did/said to annoy him and I don't like leaving things undone.

OK, I understand where you were coming from now.

thanks Rocky

Well there are some sophisticated designs in reply to your post.

However I can suggest a simpler, cheaper, more flexible and reliable one. I notice that you have specified analogue components only - why is this? This would be an *excellent* starter project for microcontrollers.

Find a small microcontroller with ADC and PWM (PIC10F222 would be OK with software PWM). Just model your step function in a lookup table. The bandwidth you have specified can easily be achieved using filtered PWM.

These things are FLASH single chip, internally clocked, SOT23-6,

-Andrew M

By the way, what's this for? - it looks like an exam question.

Actually no one yet has asked, and I was particular to word the question in a way that provided just the necessary details for a suitable (not necessarily perfect) solution. I am more than happy with the solutions given and in fact last night purchased the components necessary to implement it. But since you asked I'm more than happy to expand on its use. I know a couple who are having their first child. The mother to be is profoundly deaf and can not benefit from a conventional (wireless) audio baby monitor in order to arouse her from sleep to feed the child. I am making a circuit which takes the audio signal from the conventional baby monitor and converts it into a signal to drive a very low frequency tactile/vibration transducer which she can place under her pillow. The advantage of my design is that the amplitude of the LF vibrations are proportional to the amplitude of the audio signal (hence proportional to the volume of the baby's cry). This way she can better sense whether the baby needs attention or not. Using this in combination with a commercially available wireless video receiver will also help her to determine the child's needs. At a lower level, here is how the circuit works:

The audio signal from the baby monitor is adjusted to be approx 1V_peak and is then passed through a precision peak detector (with about 250ms decay time) to give a low frequency signal (labelled Vin in the graph in my first post) proportional to the amplitude of the original audio signal. A separate oscillator (XR-2206 monolithic func. gen IC) is set up to generate a sine wave to drive the tactile/vibration transducer at a frequency adjustable between 5-30Hz. This sine wave is amplitude modulated by Vin. The XR-2206 was chosen because it already had an AM pin on it (pin 1) which responded to +/-4V about VDD/2 (where VDD is the single positive supply rail). As Vin goes from (VDD/2)V to (VDD/2

regards Rocky

I agree, but I still think Fred should calm down. Life is too short to waste any of it being upset.

I'm more comfortable with designs in analogue right now, programming a PIC would need more of a learning curve for me. I knew the design was easily done in analog, but the solution was evading me.

Nice idea, but time is not on my side right now to learn to program this PIC.

See my last post for a description of what its for. I guess the fact that it looks like an exam question is a result of me wanting to specify the requirements in a way that really nails them down. In an exam you don't want multiple interpetations of the problem.

Rocky