konzen

hi guys,

i intend to use the ADC0804 IC as the ADC for my uni project. the datasheet says it can operate in a standalone mode. i've cr8ed a standalone circuit with LEDs to show the output. however, my circuit seems moody. sometimes it works sometimes it doesn't. i followed the diagram given but i left the digital ground out. furthermore, connecting digital ground to the supply ground does not solve my problem. any ideas?

ps: i'm trying to get it to work before interfacing it with the microprocessor

Attached Images

ADC.JPG (34.3 KB, 23 views)

ericgibbs

hi,
Show us how you are controlling/connecting the CS,WR,RD lines in the stand alone mode, how are you generating these control signals.

Do you have the digital ground connected back to the control signal source, ie: are your CS,WR,RD lines referenced to digital ground in the circuit?

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
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konzen

i've left them out as i thought it wasn't required if i just wanted to run it standalone. i guess i'm wrong? sorry i'm quite new to this. we get no help from the lecturers at all for this project.

ericgibbs

hi,
The control pins have to be connected to the correct logic levels.

Do you have the datasheet?... this should tell you how to connect for stand alone operation.

EDIT: Look at this clip from datasheet.

Attached Images

screenhunter14.jpg (14.5 KB, 13 views)

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

konzen

yeah i do but it doesn't state anywhere in the datasheet about operating it in standalone mode.

ericgibbs

hi,
The clip from the datasheet is the stand alone, free running mode!

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

konzen

what do you mean by clip?

ericgibbs

hi,
A 'clip' is a part of the datasheet that I have copied.
Its a small extract from a larger document.


Look at this 'clip' from the datasheet, I have modified it, you should now be able to follow this/

IMPORTANT: the start switch is a momentary switch, close and release!

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

konzen

oh okay. i'll rewire my circuit. one more question, since there's no microprocessor involved, does that mean i tie the D ground to the A ground?

ericgibbs

hi,
Connect the 'D' ground back to your power supply 0 Volt/Common
and connect another wire from the 'A' ground back to the power supply 0B/common .

I'll edit the clip and repost it.

EDIT: Re-look at clip, for grounds

Attached Images

Image2.gif (22.5 KB, 14 views)

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

konzen

okay thanks alot. your help in these couples of hours was more valuable than the 3 past days i spent researching on this. this week was supposedly my mid semester break. engineering students have it tough

ericgibbs

hi,
Lets know how it goes.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

konzen

lol. will update u soon

konzen

nope doesn't work. the CSbar and RDbar pins should be driven low right? also i think the INTRbar pin is driven low to stop conversion. therefore INTRbar and WRbar pins cant be tied together

ericgibbs

hi,

The INTR is an output that happens when the ADC conversion is complete and its used to re-trigger a WR [WRITE] command according to the datasheet.

The CS is chip select it must be low, RD is READ and it also must be low.

Have you fitted the resistor and capacitor to the IC?? [10K and 150pF]

Have you connected the momentary start switch?
and switched it 'once' after you have powered up?

Do you have an analog input voltage?

Do you have a Vref voltage as per the ADC note [look at the clip]

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/