Help troubleshooting a MCP23017 Port Expander

Breakout boards, sensors, other Adafruit kits, etc.

Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.
Locked
therizza
 
Posts: 5
Joined: Sat Jan 19, 2013 10:48 pm

Help troubleshooting a MCP23017 Port Expander

Post by therizza »

I have a MCP23017 I2C 16 I/O Port Expander that isn't working in my circuit. I had it working on my breadboard, but now that it's soldered up, no joy.

I've run code that scans the I2C bus, and nothing is found at 0x20, but it is finding my other 2 I2C devices.

I've also used my multimeter to do continuity testing, and I seem to have Vcc to pins 9 (Vcc) and 18 (reset), ground to 10 (GND) 15-17 (Address select), SDA to 12 and SCL to 13. Attached are pictures.

What can I try next? Is it possible I overheated the chip while soldering?
Top.jpg
Top.jpg (206.23 KiB) Viewed 634 times
In top left corner
In top left corner
Bottom.jpg (363.52 KiB) Viewed 634 times

User avatar
adafruit_support_mike
 
Posts: 67454
Joined: Thu Feb 11, 2010 2:51 pm

Re: Help troubleshooting a MCP23017 Port Expander

Post by adafruit_support_mike »

Check for continuity between the Vdd and Vss pins. It may just be a trick of the light, but there seems to be a small solder bridge between those two connections.

therizza
 
Posts: 5
Joined: Sat Jan 19, 2013 10:48 pm

Re: Help troubleshooting a MCP23017 Port Expander

Post by therizza »

Thoroughly checked and no shorts. With power I'm seeing 5V between Vcc and Vss, and between the Reset and the three address pins. I have continuity between the SDA and SCL on the mcp and my working 7-segment displays. Worse yet, I need 3 of these boards, so I just did the Arduino and I2C devices on each, and I'm getting the same symptoms on the other 3 boards. My 7-segment displays are fine and none of the mcp's are working. I tested all of the mcp's on the breadboard successfully before soldering..

Do I need pullup resistors on the SDA and SCL lines? I've seen some diagrams with 4.7k resistors, and someone mentioned 1k resistors in the datasheet. I didn't need them on the breadboard. I've tried adding 4.7k resistors to the first board with no luck, but I need to go back and check my work on that later. I'm using Arduino Pro Minis (5V and 16mhZ). I'm really stumped on these.

User avatar
adafruit_support_bill
 
Posts: 88097
Joined: Sat Feb 07, 2009 10:11 am

Re: Help troubleshooting a MCP23017 Port Expander

Post by adafruit_support_bill »

Not sure about the Pro-mini (we don't carry that model) But most Arduinos do not have i2c pullups, so external pullups would be needed.

therizza
 
Posts: 5
Joined: Sat Jan 19, 2013 10:48 pm

Re: Help troubleshooting a MCP23017 Port Expander

Post by therizza »

I've added 1K pullup resistors. I've added a 0.1 uF decoupling capacitor between Vdd and Vss. I've added 150pF capacitors between SDA/SCL and ground as shown on figure 2-1 on the datasheet. I rewired the SDA and SCL so the signal went to the MCP23017 before the 7-segment displays. No change.

I don't have a logic analyzer so the only other thing I can think to do is to desolder it and try it back on the breadboard.

I've never had a component go bad for ESD. What symptoms would that have?

therizza
 
Posts: 5
Joined: Sat Jan 19, 2013 10:48 pm

Re: Help troubleshooting a MCP23017 Port Expander

Post by therizza »

Desoldered and put back in the breadboard and... it works. So this is a design, wiring, or soldering error of some sort. I'm going to stare at them for a bit and see if I can spot Waldo.

therizza
 
Posts: 5
Joined: Sat Jan 19, 2013 10:48 pm

Re: Help troubleshooting a MCP23017 Port Expander

Post by therizza »

Whew! SDA and SCL are flipped in my wiring! Easy fix from here.

Locked
Please be positive and constructive with your questions and comments.

Return to “Other Products from Adafruit”