MCP9700 Readings flucuate
Does anyone else have this similar issue?
When using power through a USB FTDI dongle, reading are very stable (beginning part of chart showing roughly 72F), but when I plug in just the battery source at around 11PM, the readings swing dramatically as you can see. This is my hookup minus the DPT sensor, swapped in with a MCP9700 sensor.
@den2k You are getting noise from the voltage regulator. From the data sheet:
... it is recommended that a decoupling
capacitor of 0.1 µF to 1 µF be used between the VDD
and GND pins. In high-noise applications, connect the
power supply voltage to the VDD pin using a 200ohm
resistor with a 1 µF decoupling capacitor. A high fre-
quency ceramic capacitor is recommended. It is neces-
sary that the capacitor is located as close as possible
to the VDD and GND pins in order to provide effective
Thanks for the input. Just to clarify, are you talking the stepup data sheet?
But aren't the caps on the stepup module enough to dampen and stabilize the power. I shouldn't assume it does, but figure I'd ask.
@den2k I was referring to the MCP9700 data sheet.
This is the hookup I have for the MCP9700. Hmm. Any additional thoughts? I'm going to try adding a 1uF and 200 ohm resistor and see if anything happens.
Problem solved. For those interested. The issue was the 3.3V Step up board. When the radio turns on there is a large power draw which causes the voltage on the 3.3V rail to drop. This caused the temperature reading fluctuations I was seeing. I added a large cap between the Vout / GND of the step up. Problem solved.