Posts posted by windoze killa
You don't need 4 op-amps to achieve this. 2 will do it fine. You just need a circuit that will give you a zero and span calibration (this is the 1st op-amp). The zero cal will move the voltage window up or down. The span cal will widen or narrow the window, or voltage swing. You can add a span calibration with a pot in the feedback loop of the op-amp. The zero calibration adjustment can be added by connecting a vref bias to the negative input of the same op-amp. You will want to add a buffer on the output to keep other things in the circuit from effecting your calibration (this is the 2nd op-amp). The buffer is just another op-amp with no amplification. The cal can be performed by injecting 2.5V to the input and adjust the voltage reference pot at the op-amp minus input (the zero cal) until you get zero at the output. Then inject 5V into the input and adjust the pot in the feedback loop (the span cal) until you get 5V at the output. You will need to go back and forth and make the adjust a few times since the adjustments effect each other. Each time you adjust, you will notice you are shaping the output closer and closer to the shape you want. Once you see 0 out when you inject 2.5 and you see 5V when you inject 5V, then your adjustments are finished.
This is the type of circuit that has been used to shape the outputs of sensors in instrumentation for years. Most sensors are not very linear without a little help. Seems like it is almost a forgotten application since most manufacturers now scale the voltage in the source code and/or use sensors with digital outputs. Note that without a bipolar supply on the op-amp, you will not get the output to be perfect zero to five.
Is this a school project or a project for your employer?
Well I actually need 5 OP amps as there are 5 currents I need to monitor so I can get away with 2 chips.
The good news is that I have got it working with LM324s.
Bad news is we are back to 5V supply and rail to rail amps.
Hopefully I will have this sorted by the end of the week. Thanks for all the help.
yes...that i know....but the thing is that the range of significant frequencies for every song is different...
Correct. That means the fountain will spurt water differently for every song. Would be a bit boring if it didn't.
If you were to have specific filters for different ranges of frequency of the music you can have the O/Ps of the filters control different jets of water. Bit like the old musicolor light displays.
Good idea. Didn't think of that. Unfortunately I don't think we will have the real estate on the PCB. Pretty much why we are using op amps as we can get 4 in one package. And also the softies won't need to write anymore code.
Guess what. In the process of building up my circuit I have been informed (after 3 weeks of toil) that I can have a 10V rail and have to use an LM324. Not bad seeing I was supposed to have this design finished last week. Oh well back to the drawing board.
While i am trying to work this out I will be happy to accept any suggestions.
I have hooked the negative 9 volt rail to the MAX333CPP.
The voltage on PIN 3 when it is supposidly grounding is now 0.08v. Lower, but not low enough to turn off the comparator.
What is this other solution of yours?
Try putting a voltage divider with a pot on the other input to the comparator. Adjust the pot to cancel the small voltage you are seeing on the other input. You could even go a little further so you need a high voltage to switch the comparator.
From what I can find, 555 timers only seem to be able to output pulses, is this right, because I need a steady output as opposed to a pulsing one.
Thanks very much
You can make a 555 do almost anything. But what you require is a pulse, one that can be varied from 0s to 180s. You can do this using a pot and capacitors or you could do it with fixed resistors and capacitors and use a switch to select fixed delays.
Sounds like a pretty simple task. All you need is a 555 timer. There are plenty of circuits on the net that should do the job for you.
I can't think of any specific parts of the top of my head but there are heaps of ICs out there for driving 3 phase model engines. In particular brushless motors for model aircraft.
The metalic braid you are refering to is the shield of the cable and is generally connected to earth or ground. If you are talking about a cable designed for audio then you can comb the strands out and twist them together. This and the centre conductor form an un-balanced cable. You terminate it in what ever way is required in the circuit.
Now, if the cable is an RF cable then it is a slightly different matter. The metalic braid is still a shield and is always connected to ground and is also an unbalanced cable. BUT, because of the frequency of the signal the impedence of the cable and any termination will affect the amount of signal that is passed (this is also true about the audio cable but is less critical). As such any termination must be very good and the use of specific connectors is required.
Also as I have called these unbalanced cables I guess I should explain what this is. An unbalanced cable implies that the 2 conductors are at different potentials and the shield is nearly always at gound potential. A balanced cable implies that the 2 conductors are balanced and at the same potential. Although a balanced cable doesn't have a shield they still do not radiate as much as one would expect. This is because the current flow in each conductor (when terminated in the cables characteristic impedence) is equal and opposite and tends to cancel the radiation.
WOW. Now that hurts the memory cells. I could go a lot deeper but I will avoid that for now.
More than willing to continue if anyone would like.
It sounds like you are connecting a sensor to the A2D on a micro. If this is the case, you do not need to waste your time converting the voltage. Just use what you have. Adjust the reference voltage on the micro if you need better resolution.
Also, if this is not your application, I think there would be an interest in what you are making. Please share with the forum if you are able to do so.
You are partly right. This voltage will be fed into a micro but the I/P has to be 0V to 5V. The code in the micro is being used in many places and all the other inputs are 0V to 5V so we can't change the code just for this one. They are to be interchangable between each other.
I will give you a little bit more info for this project. I have a bunch of current sensors measuring various rails of a power supply. The current sensors have an O/P of 0V to 5V for the range of current. Unfortunately 0A equals 2.5V. Negative current is 0V to 2.5V and positive current is 2.5V to 5V. We are only interested in the positive bit. The problem is we need a current sensor that has a 5V supply and can handle 25A. These are the only ones available
in this range.
A good rule of thumb concerning power supply caps is 10 uF per amp. Seeing as you require 6A then 60uF would be a good choice. As 60uF isn't a standard value the 47uf or 68uF would do the job. Capacitance is really only critical in switch mode PSUs. If you decide to go with a SMPS then I would think 100uF or higher maybe needed. Sometimes it is required to use a few caps in parallel to lower the ESR.
But can we have a bit more info. Type of amp? Audio? RF? Type of active device?
I now realize I was being a bit lazy about the circuit I described, I used an online opamp calculator to provide the starting values but they aren't quite correct.
What I have done is obtained some AD8601 rail-rail single supply opamps and did a quick build using a 500K pot as the feedback element and a 50K pot to derive the reference.
You probably don't want to connect them in series. In this configuration if one fails none of them wil remain lit. This will also mean you will have to check each one to find the dead one. If you have them in parallel then only the one that dies will be unlit. Although these LEDs have a built in 470ohm resistor it maybe wise as already stated to include another. I would use a potentiometer on one so you can adjust it to an intensity you like and then measure the resistance and then replace it with a resistor that is close to that value. You would put this resistor into each LED leg.
Something I always suggested to my students when they asked for a project was test equipemnt. Build yourself a capacitance meter or function generator or frequency counter. They are always usefull.
Thanks Pebe but I am not denying that it may work. It just doesn't seem to work in Altium designer simulation. When you pay $10K for a program you expect it to work. I am still obviously missing something.
I have also put your other simpler single amp into Altium as well and it doesn't seem to work either. I can see I am going to have to do this for real. I was trying to save time and money and use the tools we have at our call but obviously I am doing something wrong. Also my OP AMP theroy is a little rusty. I will certainly be posting the results here so you know how I go.
Even if I don't get this solved thanks to everyone thats tried.
Pretty much yes. So long as you observe the power requirements of the earphone.
Well we need a load resistor. This shall be driving into an analog I/P of an AVR.
With a load of 100K I get an steady O/P of 1.5V.
1M gives an O/P of 0V
No load gives an O/P of 5V
This doesn't make sense. I am obviously missing something. I shall pull out that dusty 20yo book and read some more.
Still have a steady DC output but this time it varies withe the value of the 2 resistors and the load resistor. My head hurts.
I haven't been able to build this but have tried to sinulate it in Altium designer. It gives a steady output of 120mV. I have tried to vary the values but it stays at a steady O/P around 100 to 150mV. My OP AMP theroy is obviously very depleted. Any more suggestions or variations??
Thank you. I think that is so close to what I have been trying to do. Will give it a try during the week.
I am try to work out how to take an I/P voltage that is between 2.5V and 5V and produce an O/P of 0V to 5V. I only have a +5V supply to work with which is where I am having the problem. I have tried everything but just can't come up with an answer.
There has to be someone that can trip over an answer.
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The 72W is probably 72W PMOP which basically translates to the O/P power just prior to melting. There is really only one power measurement and that is RMS. It would be handy if you can find out what the RMS power of this amp is. Would be much easier to say if the speakers will handle it. If the speakers are a decent brand then the power of the speakers is probably in RMS and can probably handle the amps O/P.