Unknown component

[adrianvon]

Hi all,

This is my first post in this forum.

So basically i want to use an 8051 microcontroller where I will have two input buttons (up and down). Every time the up button is pressed, the output of this 'unknown component' will increase by 10mV. When the down button is pressed, the output will decrease by 10mV. (please see attached photo)

Can someone please help me in what component to use that will increase and decrease the output by 10mV every time the input buttons (up and down) are pressed ??

all kind of help will be appreciated

Thank you in advance
Adrian
(Malta)

 

[Reloadron]

What you seem to be getting at using is a D to A (Digital to Analog) chip. When the count input is incremented up one count the output will increase and when the count is decremented the output will decrease. You don't mention a maximum voltage out? There is more to it but in a nutshell that is all you need for the voltage out. You would not need a 8051 for the buttons unless you specifically want one in there for other reasons.

Oh and welcome to the ETO forums.

Ron

 

[adrianvon]

Thanks Ron for your fast replay and for your welcome . Do you have a similar diagram/schematic of an AtoD converter which is used in a similar situation?? since im not into AtoD converters :S
By the way, the 8051 is going to be used since the value will be displayed on an LCD (for instance if the up button is pressed, the value on the LCD will go from 28 to 29 and the output voltage will increase by 10mV).

The maximum output voltage will be 1.2V and the minimum output voltage will be 500mV.

 

[Reloadron]

I can probably give you a rough schematic. I am at work right now. Someone else may come along in the meantime with a circuit or better thoughts.

Ron

 

[adrianvon]

Ok thanks for your help Ron At the meantime i will do some research on A to D converters.

 

[alec_t]

i will do some research on A to D converters.

It's D to A you want; not A to D.

 

[adrianvon]

sorry my mistake

 

[Reloadron]

Yeah, D to A and maybe a chip like the DAC0808 would be a candidate.

Ron

 

[adrianvon]

But when using a D to A you will have a limit of steps (for instance can increase for 8 times only). Am i right??

 

[crutschow]

But when using a D to A you will have a limit of steps (for instance can increase for 8 times only). Am i right??

A D/A has a minimum resolution based upon the number of control bits. Thus an 8-bit D/A has a minimum resolution (step) of 1 bit or 1/255 of full scale. You didn't say how high you want to voltage to go so I can't tell you how many bits you need for 10mV resolution. For 8-bits and 10mV resolution, the full-scale value would be 2.55V.

 

[Reloadron]

Yes, there is a step limit. The way it works is for example a simple 8 bit D / A will have 8 bits (2^8) quantization levels. That becomes 256 steps (0 through 255). The chip I suggested for example is a 8 bit D to A. This is the data sheet for the DAC0808 8 bit D/A converter. If you look at the data sheet you will see the chip has 8 address lines (A1 through A8) and it also has a Vref - and a Vref + input. The Vref determines the span of the output. You want to increment or decrement the output in 10 mV steps between 500 mV and 1500 mV for a span of 1 volt so you would need 1 / .010 = 100 steps looking at it that way. Also Vref - would be 500 mV and Vref would need to be 3.06 volts.

You need a driver scheme. You may want to cascade a pair of 74HC192 BCD up down counters. That is a programmable up / down counter where each of two would give you 4 BCD outputs for the 8 address lines of the D to A converter. Unless there is a way you can do this with the 8051 which I would be useless with as to help.

Left work early today, saw the doctor and I have acute bronchitis which explains why I feel lousy. If you think the 8051 can do the work we do have a good micro-controller section with a sub section for the 8051. You may want to post in that section for more ideas. The 74HC192 counters could be programmed for the 100 counts I believe.

Maybe another member has some thoughts?

Carl, just saw your post. I think he wants to go from 500 mV to 1.5 V in 10 mV steps from what I read. I am just not feeling well so my brain isn't with the program.

Ron

 

[adrianvon]

Thanks everyone for your help, especially for you Ron. Your post was very detailed and informative.
Can i use a digital-potentiometer such as the DS1869 instead of a D to A ?? (please see attached picture) much easier and practical i think, although i never used it.

By the way get well very soon Ron

 

[Reloadron]

That would work but you have 64 steps. For the range you had in .010 steps you would need more steps. Interesting as I had not thought about using a digital pot.

Yeah, eating antibiotics and everything they gave me, when it kept getting worse I knew it wasn't a common cold. Thinking stay home tomorrow. Thanks for the well wishes.

Ron

 

[adrianvon]

Is it possible to set the digital pot to have a minimum resistance of for instance 1Kohms (ie from example 1Kohms to 10Kohms), therefore reducing the tap points (steps) from 156.25ohms (10Kohms / by the 64 steps) to for instance 50ohms ??

Will see the reply tomorrow at 6pm since its already 11.30 here in Malta and tomorrow i have to wake up at 6 for work. Good night and thanks again

 

[adrianvon]

Does a 500ohms digital pot exist?? i cannot find online :S they all start at 1Kohms

 

[Reloadron]

Hi adrianvon

All of the ones I am familiar with begin at 1 KΩ. I have seen them in a variety of "flavors" for example this listing from Analog Devices. Unfortunately I haven't had an application to actually use them.

This is an example of using an Arduino uC with a programmable digital pot. You may find it interesting as it is an addressable digital potentiometer.

Ron

 

[adrianvon]

Thanks for that list.
The problem is that we cannot use an Arduino for the project since it is easy to program...

 

[Reloadron]

The Aurduno was just used as an example. Hopefully the linked data sheet will help you out. If you can do this using a digital potentiometer it will really cut down the parts count. That would be sweet!

Ron

 

[adrianvon]

Ok im going to use a DAC .... still waiting for it to arrive from England, since nobody have them here in Malta :S Thanks for your help guys