Tuesday, November 20, 2012

Hacking your own PCB

I mentioned a problem with the LM4140 reference voltage as a poor design decision. Adding a capacitor didn’t solve it nor did adding a resistor. Realizing I was unhappy with this I decided to hack the board and put on a voltage divider for the reference voltage.

I explained before but the short is you need a voltage reference in between the +ve voltage and the ground in order to have a single sided amplifier. This reference raises the differential voltage from the strain gauge.

I’ve attached a picture of the old reference resistor and the hack of two resistors and a bridge wire. It’s giving much better stability.

So why is this ultra precise high grade IC failing… because it’s source is a poor linear regulator on the Arduino Pro Micro. So this means that as the supply voltage drifts up and down that means that relative the reference it’s drifting. This is now ratiometric and even if the supply drifts the reference is still at the same “relative” voltage keeping it all nice and stable.

I seriously hate magnetic reed sensors. I dislike how I have to program the microcontroller. V4 will have a MEMs gyro.


I spent yesterday figuring out how would I program the nRF51422 if I switched to that for development. Kicking myself for missing out on the free board Nordic offered, but even more so for not getting the free day of training. That could be invaluable. However, my self learning has revealed that the nRF51422 is not as scary too deal with. Segger J-Link to 9 pin “JTAG” (not true JTAG as I understand it for the nRF51422 which actually uses a two pin arrangement to program, but it does contain the normal JTAG lines) is all there is to it.

A big issue with this is that if I don’t incorporate an OEM J-LINK means others can’t reprogram it. Mixed feelings on this. Let me know your thoughts? I haven’t decided if V4 will be a minor increment or more major. Feel free to let me know your thoughts via email.

No comments:

Post a Comment