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Project using Opamps-intermediate level

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Winsu

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Hi All,

I would like to do a project with many op amp. I want to do it to educate myself, I need a project that challenge me a bit but something achievable for someone with intermediate experience. Does anyone have an interesting idea?.


Thanks in advance,
Winsu
 

Hi Schmitt trigger,

It seemed a good idea as it uses several op amp. I have done a little bit of a research and I have seem schematics with 10 op amp ( channels ) and it looks interesting. The problem is that the configuration for each op amp
would be the same just changing the peripheral components to boost or attenuate specific frequencies. I was actually trying to find something that combines different types of configurations on the same circuit such as comparator, adder, differential, inverting in the same circuit. I have searched for things like a fire alarm or things like that and all of them just have 1 op amp or 2 maximum. I wonder what I could do with different types of configurations? Thanks again.

Winsu
 

Suggestion: an analog calculator. One or two voltage inputs and one voltage output.

You could implement add, subtract, multiply, divide and possibly log and square root functions by using op-amps in different combinations and with different feedback elements.

Brian.
 

Winsu said:
Hi All,

I would like to do a project with many op amp. I want to do it to educate myself, I need a project that challenge me a bit but something achievable for someone with intermediate experience. Does anyone have an interesting idea?.


Thanks in advance,
Winsu
Click to expand...

I am intrested :thumbsup:
 

Thanks Betwixt,

I could do something like that and I think it would help me to learn. I have just got a power supply with one single output but I have though that I could use a DC-DC buck converter to step down the voltage to 5V then ,I would always have a variable voltage as V1( from the power supply) and a fixed voltage of 5V as V2, then I have V1 and V2 to do operations.

- - - Updated - - -

thannara123 said:
I am intrested :thumbsup:
Click to expand...



Are you planning to do any specific project?
 

Simply use two potentiometers, both wired across 0V and supply. That way you have two independent variable voltages with only two components being used!

Do be careful with the supply voltage for the op-amps, although many will work at 5V these days, some of the older ones need a higher supply voltage and for some operations it is useful to have a negative supply as well as a positive one. Another thing to consider is the maximum and minimum output voltage the amps can produce. Many are not 'rail-to-rail' so you may find the output is restricted to a little above ground and a little below supply or are not linear when they approach the output limits. It varies by device but something to watch out for, especially when used for mathematical operations.

Brian.
 

Hi Betwixt,

Thanks I will take those tips in consideration. To achieve a negative voltage I am not sure how I would do it, my power supply doesn't supply negative voltage, it is just from 0V to 30V. I guess I could use an inverting buck-boost converter or there would be a much simpler way?

Winsu.
 

The easiest way to produce a FIXED negative supply is to use a commercial inverter module. There are many with 5V in and 5V out or with 12V in and 12V out. As the output is isolated from the input, you can join the '+' output to the input '-' and it will produce a split supply with no other components needed.

Alternatively, as the current is likely to be quite small, you can use an NE555 and negative voltage charge pump with just a few components or you can configure most small switch mode regulator ICs to produce a negative output.

Brian.
 

Thanks Betwixt. I'm not quite sure what do mean by the '+' output to the input '-' . I take the + output is the output from the inverter module but the - input?, is it the negative input of the power rails of the op amps?
 

The inverters (NME0505 etc.) take DC in and produce DC out, they are very small, about 10mm x 15mm x 6mm and have four pins. The two output pins are electrically isolated from the two input pins. If you use 0V and +5V from your PSU as the positive op-amp supply and also feed it to the input of the inverter, you can connect the positive side of the inverter output to 0V and use the negative output as -5V.

+5 to inverter +5V input and op-amp +5V
GND to inverter 0V input and inverter +5 output and to op-amp 0V
inverter 0V output to op-amp -5V.

Brian.
 

Hi Betwixt,

I understood, thanks. I think I have got now a project that combines a few things and uses many op amps. I will post here schematics when they are done.... thanks again.

Winsu.
 

Hi Betwixt,

I am finally starting with my project. I am simulating with success adding and subtracting operations but the multiplying operation is not being a success. I have found and schematic from this link:

https://en.wikibooks.org/wiki/Electronics/Analog_multipliers

I wonder if this just works when the input voltages are just 0.7V or below as it is the log region of an diode?. If the input voltages are not below 0.7V the op amps are not working on the log region and the multiplying operation cannot be done.

Is there any other way to use op amp to multiply without using the log function?. I know multiplication is ultimately a sequence of addition but using that way I will have to use a huge number of op amps.
 

Hi,

personally I don´t like analog multipliers, I´d rather use the digital solution. Thus I´m not an expert in this area.
But if I had to do analog multiplication I´d use ready to buy "analog multiplier ICs".

I see you want to use "many Opamps" .. I´m not sure if you want to use "only Opamps"..

Klaus
 

Hi,

I did think about that analog multiplier ICs but they are quite expensive. They are about 9-10 pounds per ICs, it is a bit price for a project for fun. I am thinking to implement other functionalities with op amp. The problem I don't know which ones. I am thinking to implement a current source that can be regulated with a pot.

Thanks.
 

Hi,

I second Klaus, buy the part or go via software, if needed for a purpose, for learning - very pleasant and instructive.

A good application note:
AN-31 Amplifier Circuit Collection

It's a pdf. If you want to experiment with op amps, this is a nice collection of circuits to learn from. Figure 70, page 39: multiplier/divider that works, with the caveat that homemade analog mulipliers can't really be made to be precise, more of an enjoy the journey than expect to reach your exact destination circuit.

Current sources are nice, too. Or voltage references, or filters, or an OA window comparator comparable to the LM3914, or wave-shaping circuits, etc.

Op Amps for Everyone has details about OAs and is very comprehensive.
 

Hi d123,

Thanks for the PDF, definitely there are many circuit to do in that documents.
 


Hi Dana,

Nice books, great links, thanks.
 

Thanks. Very interesting project. I want to do the same.
 

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