extremely basic analogue calculator - Electronic Circuits Projects Diagrams Free

grrr_arrghh · 20th February 2004, 03:42 PM

Hi

I had an idea for a very simple analogue calculator.

several variable resistors in series, each is turned to an ammount, the total resistance would be the sum of the three ammounts. Its pretty basic, but its something to fill my otherwise empty life

but, my only stumbling block is how to measure the overall resistance, without using a multimeter (which would defeat the point a bit)

i'm thinking either seven sigment displays, or an analogue ammeter, but i'm not sure how to 'invert' the current (under normal circumstances, the higher the resistance, the lower the current)

maybe it could be done with a voltmeter?

all suggestions welcome

Tim

**Nigel Goodwin** · 20th February 2004, 03:54 PM

It's called an 'analogue computer', it's what opamps were invented for - way back before IC's. A meter was commonly used for a readout.

grrr_arrghh · 20th February 2004, 04:00 PM

oh...

hmm, op-amps make some sense, although it'll take me a while to think how to do it.

if i remember, epe mag did a feature on an analogue computer - this was quite complex, is this what i am going to end up trying to make (if so i'll give up now!!), or is there more simple versions that i could make?

Thanks

Tim

**Nigel Goodwin** · 20th February 2004, 09:15 PM

It depends how far you want to go, the EPE was quite limited as I recall.

The technique with an analogue computer is to simulate the function you are trying to calculate, it's where many of the opamp circuits (mixers, integrators etc.) originally came from.

Because of the analogue way they work, you generally need to wire a number of different sections together - this is why analogue computers were usually provided with lots of plugs and sockets. With a digital computer you write a program which goes into memory, with an analogue one you actually construct a circuit which does what you want.

Russlk · 21st February 2004, 12:41 AM

The operational adder:

grrr_arrghh · 21st February 2004, 01:31 PM

oh, ok thanks

i think i could probably work out some other functions out using that kind of circuit.

limited or not, that was all i was really trying to create, i just wondered if there was a better way of displaying the output (than using a voltmeter)

thanks again

Tim

nettron1000 · 22nd February 2004, 12:31 AM

Quote:

i just wondered if there was a better way of displaying the output (than using a voltmeter)

You can use a LM3914 IC (or a cascade of these) that show the voltage level on a series of LEDs.

grrr_arrghh · 22nd February 2004, 11:55 AM

interesting - thats what i'm talking about

but - how?

and ermm it seems that the LM3914 has been discontinued - is there a good alternative?

thanks

Tim

Russlk · 22nd February 2004, 12:06 PM

Go to www.digikey.com and look for "bar graph"

grrr_arrghh · 22nd February 2004, 01:39 PM

Hi, again

I constructed the operational adder that you posted (a snake that can do maths, how comedy!), using input volatages of between 5v and 10v, and the voltage at the output was only around 80mV ?????

I has assumed that if all three input voltages were 5v, then the output would be 15v (5+5+5) ?

maybe i missinterpreted what you meant? :?

**Nigel Goodwin** · 22nd February 2004, 01:59 PM

It would actually be -15V, because the circuit inverts, to correct it you would add another opamp as an inverter on the output. Obviously the output voltage is dependent on the supplies to the opamp, and it's capabilities. Just as with a digital adder you have to avoid overflow, with an analogue one you have to keep within the supply rails.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

20th February 2004, 03:42 PM	(permalink)
grrr_arrghh	extremely basic analogue calculator Hi I had an idea for a very simple analogue calculator. several variable resistors in series, each is turned to an ammount, the total resistance would be the sum of the three ammounts. Its pretty basic, but its something to fill my otherwise empty life but, my only stumbling block is how to measure the overall resistance, without using a multimeter (which would defeat the point a bit) i'm thinking either seven sigment displays, or an analogue ammeter, but i'm not sure how to 'invert' the current (under normal circumstances, the higher the resistance, the lower the current) maybe it could be done with a voltmeter? all suggestions welcome Tim

20th February 2004, 03:54 PM	(permalink)
Nigel Goodwin	It's called an 'analogue computer', it's what opamps were invented for - way back before IC's. A meter was commonly used for a readout.

20th February 2004, 04:00 PM	(permalink)
grrr_arrghh	oh... hmm, op-amps make some sense, although it'll take me a while to think how to do it. if i remember, epe mag did a feature on an analogue computer - this was quite complex, is this what i am going to end up trying to make (if so i'll give up now!!), or is there more simple versions that i could make? Thanks Tim

20th February 2004, 09:15 PM	(permalink)
Nigel Goodwin	It depends how far you want to go, the EPE was quite limited as I recall. The technique with an analogue computer is to simulate the function you are trying to calculate, it's where many of the opamp circuits (mixers, integrators etc.) originally came from. Because of the analogue way they work, you generally need to wire a number of different sections together - this is why analogue computers were usually provided with lots of plugs and sockets. With a digital computer you write a program which goes into memory, with an analogue one you actually construct a circuit which does what you want.

21st February 2004, 01:31 PM	(permalink)
grrr_arrghh	oh, ok thanks i think i could probably work out some other functions out using that kind of circuit. limited or not, that was all i was really trying to create, i just wondered if there was a better way of displaying the output (than using a voltmeter) thanks again Tim

22nd February 2004, 11:55 AM	(permalink)
grrr_arrghh	interesting - thats what i'm talking about but - how? and ermm it seems that the LM3914 has been discontinued - is there a good alternative? thanks Tim

22nd February 2004, 12:06 PM	(permalink)
Russlk	Go to www.digikey.com and look for "bar graph" __________________ see my website: www.geocities.com/russlk

22nd February 2004, 01:39 PM	(permalink)
grrr_arrghh	Hi, again I constructed the operational adder that you posted (a snake that can do maths, how comedy!), using input volatages of between 5v and 10v, and the voltage at the output was only around 80mV ????? I has assumed that if all three input voltages were 5v, then the output would be 15v (5+5+5) ? maybe i missinterpreted what you meant? :?

22nd February 2004, 01:59 PM	(permalink)
Nigel Goodwin	It would actually be -15V, because the circuit inverts, to correct it you would add another opamp as an inverter on the output. Obviously the output voltage is dependent on the supplies to the opamp, and it's capabilities. Just as with a digital adder you have to avoid overflow, with an analogue one you have to keep within the supply rails.