New Compact Prototype

Latest compact board is back from OshPark ( and testing is complete. Using the base Adafruit transimpedence amp design we were able to come up with a simple formula for convert the raw ADC values into a UVI. We’re debating whether or not it’s worth it to come up with a resistor divider which gives a bit more signal, but basically doubling the ADC readout and then dividing by 100 does give us plenty of headroom in case someone encounters some really crazy UV exposure. Additionally, we added a slow on-off warning blink should the ADC return a maxed-out value.


New UV Sensor Testing

The Roitner Technik GUVA-S12D is too expensive for a product hoping to cost less than $10 each. So I am looking for more cost effective alternative.

Here’s the test rig, consisting of a GUVA-S12D, a VEML6070, and an unspecified LED acting as a light sensor. The ADC reading seems to track the UVI produced by the GUVA-S12D quite well up to UVI 5. From there up to 6.5 (the highest I have measured outdoors) it is a bit lower.

My LED under test shows good visible light blindness. It responds quite strongly to a 365nm UV LED (as does the VEML6050). This might be due to the spectral distribition of the LED. I’ll be looking around for a local lab to quanitfy the response of all three under controlled conditions.

Previous UV Monitor Size Comparison

Here’s the older UV Monitor v 1.2. This one used the same GUVA-S12SD UV sensor, but used it to calculate an accumulated UV dose and warn the user when they are about to get to a dose causing sunburn. Primary issue here was inability to control orientation and therefore the indicdent UV level. Pretty much the only way to use it and get accurate results was to attach it to the brim or top of a hat.


UVI Meter Project

I’ve been working on a simple solution for ultra-violet exposure awareness and mindfulness. Previous solutions offered dose monitoring, but the main problem here is the difficulty in keeping it oriented so as to achieve proper incidence – hard to to in a wearable. Also, the reality is if you just put on sunblock or wear protective clothing, you don’t have to worry about it.

So the main problem is mindfulness; if you get people thinking about UV exposure maybe they will do a better job of taking action. The latest device takes this into account. All it does is measure the current UVI. It’s cheap, pockeable, and has room for instructions and medical provider/sponsor info.

Here’s a photo of the prototype:



Prototype production is underway with a goal of 20 boards. Sounds pretty small, and it is, but I’m hand-applying solder paste to pads and acting as my own pick-and-place machine. It takes time to populate a board! Later runs will either offshore the whole board or at least panelize and use a solder paste stencil.

wordpress install not letting me see uploaded images

My brand-new WordPress install was letting me upload images just fine, but would only show them to me in editor mode. Otherwise it displayed an “?” icon.

After much digging and checking of file ownership/permissions, I found the answer:

My apache2 2.4.5 requires “require all granted” directive, in addition to “allow from all”.

/etc/apache2/sites-enabled/wp.conf now looks like:

Alias /wp/wp-content /var/lib/wordpress/wp-content
Alias /wp /usr/share/wordpress
<Directory /usr/share/wordpress>
Options FollowSymLinks
AllowOverride Limit Options FileInfo
DirectoryIndex index.php
Order allow,deny
Allow from all
<Directory /var/lib/wordpress/wp-content>
Options FollowSymLinks
Order allow,deny
Allow from all
Require all granted