# How do I use an Arduino to write say 2.1 volts? Hobo dataloggers accept 0-2.5vdc inputs. Arduino outputs PWM.. thanks!?

I'm working with a university and they love their Hobo's and I don't blame them... they're pretty straight forward to use...

I'd like to write to the Hobo... here's the hobo analog inputs: 0 to 2.5 Vdc; 0 to 5 Vdc; 0 to 10 Vdc; 4-20 mA

Hobo stats: http://www.onsetcomp.com/products/data-loggers/u12-006

Analog channels: 0 to 2.5 Vdc; 0 to 5 Vdc; 0 to 10 Vdc; 4-20 mA

Accuracy (logger only): ± 2 mV ± 2.5% of absolute reading; ± 2 mV ± 1% of reading for logger-powered sensors

Resolution: 0.6 mV

Sample Rate: 1 second to 18 hours, user selectable

Time accuracy: ± 1 minute per month at 25°C (77°F), see Plot A

Operating range: -20 to 70°C (-4° to 158°F)

Operating temperature:
Logging: -20° to 70°C (-4° to 158°F)
Launch/readout: 0° to 50°C (32° to 122°F), per USB specification

Humidity range: 0 to 95% RH, non-condensing

5 years ago
The short answer is that you feed that PWM signal through a simple low-pass filter, the kind made from just  a resistor and a capacitor.  Such a filter will take out the quickly switching on-off, AC component, of your PWM signal, and leave only the DC part,  which is just the time averaged voltage.

guessing maybe  someone had already gone to the trouble of explaining this topic in greater detail, and I found this page, which is specific to the topic of low pass filtering your Arduino(r) 's PWM outputs.  Um, here:

http://provideyourown.com/2011/analogwrite-convert-pwm-to-voltage/

And I'm hoping that page will tell you everything you want to know, or at least get you going in the right direction.
;-)
hydronics (author)  Jack A Lopez5 years ago
thanks!
frollard5 years ago
hokai...

so put a big smoothing capacitor and resistor on the analog output and you have a value from 0-5 volts. Make it into a resistor divider and you can make it go from 0-2.5 volts.

Most serious question, why not get a sensor that outputs an analog value? An arduino (atmega) isn't a particularly good sensor. If you already have an analog output sensor then you could again use a resistor divider to drop your (probably) 5 volt output to a loggable 2.5
hydronics (author)  frollard5 years ago
thanks for taking the time to answer!!