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ECET 297 Fall 2009 Digital Volt Meter

8. Future Plans

posted Feb 14, 2010, 7:22 PM by Bill Bai

I was pretty disappointed that I couldn't get the autoranging functionality working on my DVM.  I wasn't able to correct the issue in time for the end of the semester, but now I basically have all the time in the world to fix it.

I'd also really like to build a small board using only surface mount chips and parts.  I think that it would be more than possible to fit all of the parts under the LCD, thus making the full size of the DVM only as large as the LCD (3.695"x1.800", LCD datasheet attached).

7. Final Report and Issues

posted Feb 11, 2010, 11:45 PM by Bill Bai

The basic voltmeter functionality of the board worked very well.  All of the measurements in all ranges had less than <1.3% error.  

However, the auto-ranging function encountered some issues. The auto-ranging clock is based off of a square wave generated at the Cref+ pin.  The square wave is supposed to be a 500mVpp signal, but it actually turned out to be 100mVpp, likely due to output loading.  A set of transistors was supposed to step this square wave up to TTL logic levels.  But since the signal was too small, this didn't work and thus the auto-ranging clock never actually clocked, defeating the auto-ranging.

There were also two small details in the PCB layout that caused problems. 
I had put this chip on the wrong side of the board so I put the socket on the right side and bent the pins of the IC back to fit in the socket.  As you can see, that is the bottom of the middle chip rather than the top.

In this other case, the IC's turned out to be a bit bigger than was expected.  I had to bend the pins again to make both IC's fit.

6. Final Printed Circuit Board

posted Feb 11, 2010, 11:28 PM by Bill Bai   [ updated Nov 2, 2010, 3:38 PM ]

Final PCB with LCD installed.

Final PCB without the LCD.  Note the surface mount SO-14 chip that is under the LCD.  The SmallOutline-14 (SO-14) chip is basically the same chip as the other larger DIP-14 chips with a much smaller footprint.

4. Breadboarding

posted Feb 5, 2010, 6:09 PM by Bill Bai

Here's my circuit all breadboarded out.  I ran all the leads connecting the 7106 and LCD under the LCD to make it look nicer.  I also had to add on a small breadboard at the bottom because I ran out of space for all of my IC's.

5. PCB Layout

posted Feb 3, 2010, 9:45 PM by Bill Bai   [ updated Feb 5, 2010, 6:20 PM ]

After much elbow grease and hard work, here is the final PCB layout with all copper and silkscreen layers.  I placed all the components and routed all the traces by hand.  It was rather tricky and tedious at first, but I soon worked out a method to my madness.  As you will probably notice in the top and bottom copper later close ups below, I tried to route all my horizontal traces on top and all my vertical traces on the bottom layer.  The work was complicated by the amount of IC's required to implement the auto-ranging functions.  This resulted in a huge amount of vias, but it simply couldn't be avoided.

Here's the final 'Design Status Report' generated by PCB Artist.

Design Status Report

Report File    : H:\Documents\Purdue Homework\(7) Fall 09\ECET 297\297 DVM Project (PCB - Design Status Report).txt
Report Written : Wednesday, February 03, 2010
Design Path    : H:\Documents\Purdue Homework\(7) Fall 09\ECET 297\297 DVM Project.pcb
Design Title   : 
Created        : 10/9/2009 23:02:58
Last Saved     : 10/23/2009 20:49:28
Editing Time   : 1362 min
Units          : mil (precision 0)

Board Area
22600000 mil squared

Name               Type            Side     Net

Top Silkscreen     Silk Screen     Top                     
Top Copper         Electrical      Top                     
Top Solder Mask    Solder Mask     Top                     
Documentation1     Documentation   Top                     
Top Paste Mask     Paste Mask      Top                     
Bottom Silkscreen  Silk Screen     Bottom                  
Bottom Copper      Electrical      Bottom                  
Bottom Solder Mask Solder Mask     Bottom                  
Documentation2     Documentation   Bottom                  
Bottom Paste Mask  Paste Mask      Bottom                  

Component List
Comp Type     Package     Components   Pins

R               SM              27      54     
C               SM              9       18     
ICL7106CPL      DIP40           1       40     
4023            DIL             1       14     
4071            DIL             1       14     
4011            DIL             1       14     
4016            DIL             2       28     
D               DSC             3       6      
2N3702          DSC             1       3      
4029            DIL             1       16     
4028            DIL             1       16     
H4101B          DIL             1       20     
2WPHDR          HDR2            1       2      
297TestHeader   DIL             1       14     
NO PushButton   USER            1       2      
9V Battery      USER            1       2      
3WPHDR          HDR3            2       6      
H4101A          DIL             1       20     
4030            SOL             1       14     
LED             DSC             4       8      
1WPHDR          HDR1            11      11     
4077            DIL             1       14     
MMBF170         SOT23           2       6      

Total:                          75      342    

Net List
Net Class     Nets  Track Length  Vias  Connections   Con Length

Signal          89      228339       180     0          0           
Power           1       0            0       0          0           

Total:          90      228339       180     0          0           

Drill List
Drill Diameter  Holes

24              180            
30              8              
32              179            
35              23             
35              40             

Total number of drill holes 430.
Total number of free pads 0.

End Of Report.

And finally, the good stuff you're actually looking for: pretty pictures.

Top and Bottom Copper Layers.

Just the Top Copper Layer

Just the Bottom Copper Layer.

And for those of you dedicated enough to scroll down this far....
Top Copper and Silkscreen.

Bottom Copper and Silkscreen

3. Schematic

posted Feb 3, 2010, 8:15 PM by Bill Bai   [ updated Feb 10, 2010, 7:33 PM ]

We used PCB Artist from Advanced Circuits to make the schematics and PCB layout for our boards.  Advanced Circuits is a PCB manufacturing company based in Colorado.  They do a bit of everything, but they have a really nice deal for students and everyone from ECET uses their service.  Their special deal for students is $33 for a double sided PCB up to 60 square inches, which is a pretty fantastic deal.  Not to mention a free and fairly powerful schematic/PCB software.

It's pretty hard to see the parts on the schematic above, but it's basically the circuit from Intersil Application Note 046 (attached to this and the last post, schematic from the app. note below).  There are some small changes and adaptations to make the PCB layout work better (1-pin headers for test points and 3-pin headers for potentiometers because the potentiometer footprints in PCB Artist suck), more pictures of parts of the schematic below.

The basic chip parts.  RC resonant circuit for the clock, battery, on/off switch, auto-zero and integrator capacitors, reference capacitor, etc.

7106 to LCD connections.

Over/Under Range Detection, Decimal Point detection circuitry

Switches for changing the resistors for various ranges

Register to keep track of what range the 7106 is in and the decoder to select the proper resistors for that range.

2. Auto-Ranging Digital Volt Meter

posted Feb 2, 2010, 6:21 PM by Bill Bai   [ updated Feb 4, 2010, 12:06 AM ]

I had found an application note that gave a basic design for a 4 range DVM based on a 200mV base range.  This is the application note that I started my design from.

1. ECET 297 Semester Project

posted Feb 2, 2010, 1:26 AM by Bill Bai   [ updated Feb 4, 2010, 12:05 AM ]

This project was from last semester, but it was still pretty fun and interesting, so I'm going to post up some of the materials I used and generated working on it.

The entire design is base on the very versatile ICL7106 chip (Datasheet attached).  It works by comparing an input voltage to a set voltage, then converting the output from analog to digital and putting the result on a 3.5 digit LCD display.  More information is on the datasheet and application note 017 (an017).

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