Brad Fernandez Build Log


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.


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


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


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.


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


Looks great! Keep it up!


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.


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.


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.


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.


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.