Brad Fernandez Build Log


#1

Hello Everyone!

My name is Brad Fernandez. I am from Tampa Fl. and I have been heavily involved in electronics for about three years. I have had good success with programming developer boards and now I want to move forward to designing and buidling my own.

I have already completed getting to blinky and I am currently looking at the CE Header course.


#2

Welcome Brad.I look forward to hearing more of your progress,


#3

Well I finished the layout portion of the CE Header. I Have ordered my boards from Osh Park. Now on to the Sensor board.


#4

Ok here is a little progress I made. I adapted the CE Header lesson and here is the schematic for a photon header adapter. Working on the footprints next.


#5

CE Header to Photon adapter. Well that was fun. Here is the final footprint I will be sending off to Osh Park.


#6

Looks great! Keep it up!


#7

OK Another night of work down. I got my AD2 today so I played around with that for a little while. It is a neat and surprising powerful tool. Then finished my Sensor board schematic and got all the foot prints chosen.


#8

It looks like it is coming together. One thing to watch though, on the DS7505, the data sheet makes the comment

Bus Idle or Not Busy: Both SDA and SCL remain high.
SDA is held high by a pullup resistor when the bus is idle,
and SCL must either be forced high by the master (if the
SCL output is push-pull) or pulled high by a pullup resistor
(if the SCL output is open drain).

In my case, I used a Teensy and this was a trap I fell into. I had to add 4k7Ω pull up resistor to each of the SDA and SCL lines before I could talk to the DS7505.


#9

The SCL and SDA lines of the I2C bus always require pull-up resistors as it uses open-drain/open-collector line drivers. Depending on the length of the bus, the bus voltage and the max speed of the bus you might want to use stronger pull-ups, such as 1K for 3V3 or 1K5 for 5V. The pull-up resistors have to overcome the parasitic capacitance of the line at the max frequency.


#10

Good catch. Thanks guys. I added the pull-up resistors to my sensor board last night. I’ll post pictures of my layout and schematic later tonight. I was tired last night and forgot to post my updates.


#11

Alright I finished up my layout and ordered the sensor board from osh park. I also ordered some headers and a resistor/capacitor book. Now I wait! Here are pics of my final schematic and layout. I’m going to move on to simulation while I wait for parts.