{"id":645,"date":"2013-08-29T19:40:04","date_gmt":"2013-08-29T17:40:04","guid":{"rendered":"http:\/\/paluweb.nl\/?p=645"},"modified":"2013-08-29T19:40:04","modified_gmt":"2013-08-29T17:40:04","slug":"work-in-progress-getting-the-raspberry-pi-to-talk-to-the-canopy","status":"publish","type":"post","link":"https:\/\/www.paluweb.nl\/?p=645","title":{"rendered":"Work in Progress: Getting the RaspBerry Pi to talk to the Canopy"},"content":{"rendered":"


<\/p>\n

In my previous post<\/a> I managed to program the chips in the Canopy. Now I can adjust the code inside the Canopy where needed. Next thing to get working is to allow the Raspberry Pi to talk to the chips inside the Canopy.<\/p><\/blockquote>\n



\nRaspberry Pi, Atmel AVR and serial communications<\/strong><\/p>\n

Luckily the Raspberry Pi has a serial port, because the AVR controllers I used have one too, and they use this serial port to get commands from whoever is controlling the bus… Which should be the Raspberry Pi. <\/p>\n

Problem is that the Raspberry Pi does not have a true RS232 serial port: the signals are there (on the GPIO headers), but they have 0-3.3V levels and they are inverted form the RS232 signal. Luckily the serial transmissions the AVRs in the Canopy expect are also inverted, but on a TTL (0-5V) level. Just connecting them up together will break stuff… Or maybe not?
\n

\nBuilding the simplest interface possible<\/strong><\/p>\n

I started out with 74HCT540 chips to buffer the signals and convert their levels… But in the end I basically just connected them together. Why doesn’t this break things? Simple:<\/p>\n

    \n
  1. The signals transmitted by the Raspberry Pi are 0 and 3.3V, well within the allowed levels of the Atmel AVR controllers (0-5V). Also, the AVR consider anything above 0.6 volts to be a logical “one”, so 3.3V is more than sufficient.<\/li>\n
  2. The signals received by the Raspberry Pi would normally damage the RPi, as the 5V logic “high” is way above the 3.3V it accepts as a maximum. But because I have multiple AVR controllers on a single bus, all chips have a diode that effectively pull the voltage down for a zero, but RELEASE the wire for a high. So I could just mount a single pullup resistor to the +3.3V of the RPi, and now I receive serial signals between 0 and 3.3V.<\/li>\n<\/ol>\n

    Problem solved! Now to build this “converter” in a way that it won’t break, AND fits into the RPi’s houseing. I think it worked out fine:<\/p>\n

    \"Raspberry<\/a>

    Raspberry Pi with my serial communication “level converter”. It still fits in the RPi’s housing, so I’m happy.<\/p><\/div>\n

    After connecting it all up, I mounted the RPi inside the Canopy. What a tiny little controller it is inside this big wooden box:<\/p>\n

    \"Let's<\/a>

    Let’s play “find the RPi”! It sits neatly between the LED light sources, just under the power supply.<\/p><\/div>\n

    From here, it controls all 12 AVR controllers inside the Canopy. These controllers look like this:<\/p>\n

    \"AVR<\/a>

    AVR Controllers inside the Canopy. Note the grey cable looping through all controllers to form a shared serial bus.<\/p><\/div>\n

    So what does the entire Canopy look like now? Check it out!<\/p>\n

    \"The<\/a>

    The entire Canopy with lights burning (not at 100%). Well almost… I just noticed I burnt a halogen in the bottom left :S<\/p><\/div>\n","protected":false},"excerpt":{"rendered":"

    In my previous post I managed to program the chips in the Canopy. Now I can adjust the code inside the Canopy where needed. Next thing to get working is to allow the Raspberry Pi to talk to the chips … Read more »<\/span><\/a><\/p>\n","protected":false},"author":12,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[17,8,3],"tags":[143,155,153,123,150,152,151,154],"class_list":["post-645","post","type-post","status-publish","format-standard","hentry","category-automation","category-lighting","category-paludarium","tag-atmel-avr","tag-interfacing-rpi-to-atmel-avr","tag-level-converter","tag-raspberry-pi","tag-serial-port","tag-serial-port-atmel","tag-serial-port-raspberry-pi","tag-ttl"],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.paluweb.nl\/index.php?rest_route=\/wp\/v2\/posts\/645","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.paluweb.nl\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.paluweb.nl\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.paluweb.nl\/index.php?rest_route=\/wp\/v2\/users\/12"}],"replies":[{"embeddable":true,"href":"https:\/\/www.paluweb.nl\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=645"}],"version-history":[{"count":7,"href":"https:\/\/www.paluweb.nl\/index.php?rest_route=\/wp\/v2\/posts\/645\/revisions"}],"predecessor-version":[{"id":656,"href":"https:\/\/www.paluweb.nl\/index.php?rest_route=\/wp\/v2\/posts\/645\/revisions\/656"}],"wp:attachment":[{"href":"https:\/\/www.paluweb.nl\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=645"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.paluweb.nl\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=645"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.paluweb.nl\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=645"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}