Discussion in "Project Help" started by    TB    Aug 9, 2008.
Sat Aug 09 2008, 11:50 AM
#1
I'm using a Dallas 8051 (DS89C450) for my microcontroller project and it's working fine with serial and a LCD, but now I want to add a MAX192 seriel ADC to it. I have a rough idea of how to write the software for it, but I'm not sure on how to connect it to my board. (I'm a programmer, not an electrical engineer )

At the moment I use Port1 for the LCD and three pins on P3 to control the LCD. Port 0 and Port 2 are not used at all, and 5 pins on port3 are not used. I guess I can use the free pins on port3 to the ADC? If I understand the datasheet of the ADC correct I need the following pins on the microcontroller:

ChipSelect (CS)
SCLK
DIN
DOUT

But what about VRef ? (Can I connect this to VDD?)

To put it shortly (isn't this too late now? ) how do I have to connect it? Where do I need capacitors, and where do I need resistors?
Tags free pinsmicrocontroller projectelectrical engineerrough ideaadc
Sat Aug 09 2008, 03:59 PM
#2
well ..
it is generally preferred not to connect VREF to VDD.

mostly in case of sensitive ADC application u either use two separate power supplies... for Analog and digital sections or simply isolate digital ground from analog ground.

but if it is just an experiment... just add a variable resistor/pot (small value) between VDD and Vref.
u are also supposed to add a zero ohm impedance between your analog signal and the ADC analog i/p pin.(use any resistance around 50E to gain the same effect.)


Tags variable resistorohm impedancedigital sectionsanalog signaladc
Sat Aug 09 2008, 04:07 PM
#3
Have a look at this thread .. http://www.8051projects.net/forum-t8042-last.html

For Vref you can use the typical operating ckt in pg 24.It allows for a single-ended input of 0-4.096 V with a 4mV step size.
Tags cktpg
Sat Aug 09 2008, 05:08 PM
#4


Have a look at this thread .. http://www.8051projects.net/forum-t8042-last.html

sashijoseph




Thank you for the link, but it doesn't say anything about the schematics :/ I think I have a good understand of how to interface the max192 - it's the schematics I'm not sure about. Can I just connect CS, Din and Dout to three pins on my microcontroller? (eg. P3) or do I have to use some resistors, capacitors and so on?


For Vref you can use the typical operating ckt in pg 24.It allows for a single-ended input of 0-4.096 V with a 4mV step size.

sashijoseph



Hmm, I need to monitor values between 0 and +5.0V - so I have to make a divider to bring the voltage down? (eg. a 4/5 divider)
Tags cktdoutdividermicrocontrollerschematics
Sat Aug 09 2008, 07:56 PM
#5
hi TB,
i think it is sufficient to connect the control pins directly to the uC.
As for the reference i would agree with shashi and shyam that u go for 4.096 internal reference ( looks fine as it has a good temperature stability too(30ppm/deg.)).So, yes , u will have to drop ur input voltage in the ratio 4/5.

using a reference close to the supply voltage of the ADC may create some non-linearity in the conversion at the full scale level ( do not know about this ADC as i have not used it as yet, but have observed this in many other ADCs i have used. )
Tags internal referencetemperature stabilityadcsshashishyam
Sat Aug 09 2008, 09:51 PM
#6
pdi: Thank you for your reply

What about the VDD, Ground and so on - do I need any capacitors or resistors there?
Tags resistorscapacitorsreply
Sun Aug 10 2008, 04:35 AM
#7
Fig 18 in the datasheet shows just that.
In general you can directly connect VDD,unless the supply is very noisy,in which case use a 10ohms resistor(which forms a low pass in conjunction with the bypass caps) as specified in the datasheet.
Usually a 0.1uF bypass cap from VDD to Agnd pin(as close to the pins as possible) suffices.
Tags datasheetresistorpinsconjunction

Get Social

Information

Powered by e107 Forum System

Conversation

Sun Apr 11 2021, 02:48 PM
Harmancwt
only
Fri Apr 09 2021, 02:02 PM
Hong
Quality articles is the secret to interest the users to visit the site, that's what this web page is providing. christian dating sites https://datingsitesww.com
Fri Apr 09 2021, 03:53 AM
QGWIJ38V49HEBD3WXF www.web.de
I have a small question for you
Thu Apr 08 2021, 06:26 PM
Lilly
Post writing is also a fun, if you be familiar with afterward you can write otherwise it is complex to write. dating sim https://onlinedatingtind.com/
Thu Apr 08 2021, 12:35 PM
Fredericka Horn
Thanks, Fredericka Horn

Downloads

Comments

Mirza123
Thu Jun 25 2020, 03:46 PM
eunicelove124
Mon Jun 22 2020, 03:03 PM
cerouno
Tue Jun 16 2020, 05:10 PM
Marce
Sat Jun 13 2020, 09:43 PM
Davidthils
Thu May 21 2020, 12:44 PM
Jakeror
Thu May 21 2020, 01:28 AM
motorCar
Wed May 20 2020, 07:05 PM
Vordrync
Wed May 20 2020, 11:52 AM

Online

Guests: 128, Members: 0 ...

most ever online: 182184
(Members: , Guests: 182184) on 06 Aug 2010: 05:37 AM

Members: 38215
Newest member: Mirza123