The purpose of this week's group assigment is to become familiar with the test equipment in our lab. Josep told us that we have a pocket oscilloscope and a voltmeter.
We used the digital volt meter (DVM) and pocket oscilloscope to read some some votages on the SMD11c board that Marco built. We changed the blink rate on the LED by editing the sketch in the Arduino IDE and observed the voltage across the LED.
![o-scope]()
We used a pocket oscilloscope called DSO Nano v3, which is was an open source project sold by SEEED. It is no longer manufactured or supported by teh manufatcturer, but there is a community taht cintnues to make modufcations on the product.
![DVM]()
The digital volt meter (DVM) is made a NIMO electronics MY63 MUL003 meter.
##Digital Volt Meter
![DVM voltage on regulator]()
We measured the voltage in and out of the regulator. We noticed that the voltage on the output of the reulator dipped when the LED came on.
The voltage into the regulator was a steady 5 volts.
![Video of voltage across LED]()
Next we looked at the voltage across the LED and the LED and resistor. The program turned the LED on for one second and off for two secnds.
![Video of DVM across LED various parameters]()
We calculated what the votage should be across the resistor (Vdd-Vled=Vr) and then measured it to confirm. The voltage was within a few hundredths of a volt of what we calculated.
##Pocket oscilloscope
![Video of Oscope]()
We used the pocket oscilloscope to observe the voltage across the LED as we changed the parameters of the light blinking Arduino IDE sketch. The key to being able to observe the trace on the oscilloscope is setting the voltage and time scales to the right values for the signal we want to observe. The pocket oscope can only go up to about 200 khz, plenty for what we were loking at.
![One Second on 2 off]()
One second on 2 seconds off
![Another Oscope Video]()
![Yet Another Oscope Video]()
!Even one more Oscope Video]()
##Reflections and Conclusions
It seems like it would be pretty easy to short things out using the leads on the voltmeter and oscilloscope, althought we didn't. Checked the data sheet on the LM 3480 and it is short circuit protected. USB is also short circuit protected.
We didnt try to measure currents. It was surprising to see the output voltge of the regulator dip when the LED came on. The LED is only a load of about 20 ma, and the regulator is rated at 100 ma. We could build a board with jacks for pins to read current - shorted in normal use but routed through a voltmeter when you want to read current. I wonder what the actual current draw of the SAMD11C is. Looks like the SAMD11C has a minimum amp load of 8 microamps to about 1 ma when on.
