Today I ordered the parachute (a 48″ model – on the “slow and safe” side for the expected weight), a GPS antenna, power regulator for the GPS, and of course some duct tape! \u00a0Every project needs some of that! \u00a0It it’s good enough to save the Apollo 13 astronauts, it’s good enough for me!<\/p>\n
So this evening I worked on the serial comms for the flight computer. \u00a0The serial devices will be GPS (connected to the main (hardware) serial port), radio transmitter (simple to “bit bang” at the low baud rate), and the GSM phone for messaging. \u00a0The latter will need to run from a software UART. \u00a0The computer will have some logic such as “if height below 3 miles, send position every 10 minutes. \u00a0If below 1 mile send every minute”, or something like that.<\/p>\n
I have 2 options for the GSM – a Wavecom modem and a T39m mobile phone. \u00a0The T39m has 3.3V logic levels which are simple to interface to the Arduino flight computer’s 5V levels, so that’s what I did first. \u00a0I downloaded an updated software UART that runs on interrupts and is therefore less disruptive to other operations the computer will need to do. \u00a0I then set up a simple program to echo PC keyboard characters on to the phone, \u00a0and to display anything coming back. \u00a0Then I wired the Arduino to the phone using a phone pinout I found on the web.<\/p>\n
Nothing. \u00a0I could see the Arduino was transmitting, but the phone didn’t respond. \u00a0I tested the voltage levels and made sure things were as per the diagram, but got nothing.<\/p>\n
Researching more, I found another pinout reference that had different pins for the transmit and receive lines. \u00a0After quickly rewiring, everything worked! \u00a0I hate it when people post rubbish on the web …<\/p>\n
I then set up some messages to send to the phone so it would send me a message to my main phone. \u00a0Again, nothing. \u00a0Checking the phone’s menus the message was sat there in the outbox, but wasn’t being sent. \u00a0No credit! \u00a0The SIM card is one that sits in my netbook PC and hardly gets used, and T-Mobile had kindly timed it out! \u00a0Will try with a SIM card that has credit soon!<\/p>\n","protected":false},"excerpt":{"rendered":"
Today I ordered the parachute (a 48″ model – on the “slow and safe” side for the expected weight), a GPS antenna, power regulator for the GPS, and of course some duct tape! \u00a0Every project needs some of that! \u00a0It it’s good enough to save the Apollo 13 astronauts, it’s […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[4],"tags":[],"_links":{"self":[{"href":"http:\/\/www.daveakerman.com\/index.php?rest_route=\/wp\/v2\/posts\/17"}],"collection":[{"href":"http:\/\/www.daveakerman.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.daveakerman.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.daveakerman.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.daveakerman.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=17"}],"version-history":[{"count":2,"href":"http:\/\/www.daveakerman.com\/index.php?rest_route=\/wp\/v2\/posts\/17\/revisions"}],"predecessor-version":[{"id":22,"href":"http:\/\/www.daveakerman.com\/index.php?rest_route=\/wp\/v2\/posts\/17\/revisions\/22"}],"wp:attachment":[{"href":"http:\/\/www.daveakerman.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=17"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.daveakerman.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=17"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.daveakerman.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=17"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}