Richard J. Prinz

Google’s Mirror API is, beside native GDK apps, one way to communicate with Google Glass. It is based on a range of OAuth authenticated web-service methods. The default way to use the Mirror API is to present the user a Web application where he could first register his Glass using a Google account. After this step the app or service is able to send info’s like text messages, contacts, images etc. to the users Glass device. But what if you just want to make a quick test and don’t want to develop even a simple web app or you need a way to quickly send info’s from a cron job every hour?
This is where cli_mirror comes in handy.

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So you have a new quadcopter or transmitter from Walkera and found out that there is a new firmware available on the Walkera download site. Unfortunately you don’t have the UP02 and its companion UP02-Adaptor at hand but want to update regardless. In this blog post I’ll describe another way to update your device.

 
 
 
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Walkera has a lot of interesting Copters and also a lot of add on’s for them. The X-Z-18 is a simple camera module usable for example withe the Hoten-X quadcopter. Unfortunately there is nearly no or wrong documentation available on how to install and use it.

So this post shows how to install and use it. If you are interested on some internals of the X-Z-18 then have a look at this post.

The R/C transmitter used is a Walkera Devention DEVO-7.

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Based on this post which describes controlling a Flight Simulator software with your R/C transmitter the following post describes the other way round: controlling a R/C model from the PC using an Arduino UNO.

The R/C transmitter used in this project is a Walkera Devention DEVO-7.

There are two ways to control a R/C modell from the PC:

1. Using a standard R/C transmitter by using the trainer port most transmitters have (this should also work on older transmitter models). In this case the PC is responsible for providing a PPM signal which contains information’s about all transmitter channels. The PC can produce such a signal using it’s sound card or by using an Arduino connected to the PC via USB.
    

2. By using only the transmitter module which could be found especially in newer 2GHz transmitters. The transmitter module used by the Devo7 is a WK-21201RF which uses a Cypress CYRF6936 wireless USB chip. This module has just 8 pins using standard signals like MISO, MOSI, Reset, CS, VDD, GND (Pinout can be found on Google) and can be directly connected to the Arduino.

This solution uses the DSC trainer port of the Devo7 (so there is no need to open the Devo7) and an Arduino for creating the PPM signal.

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Large service providers like Google are already offering two way authentication for their services. Others like Microsoft will follow. This authentication mechanism is based on One Time Passwords OTP combined with a timing factor resulting in Timebased One Time Passwords TOTP specified in RFC-6238.

But it’s also possible to provide two factor authentication for self written services. The provided package can be found in the following repositiory:

MCHttpRepository
	location: 'http://www.min.at/prinz/repo/totp'
	user: ''
	password: ''

It provides a simple way to create and validate TOTP’s for a given time or a time window.

" Enter the shared secret here. This is for example "
" the secret you will get if  you change your Gmail "
" account to two way authentication "
key := TOTP decodeBase32: 'qqmholtfsmddokpy'.
" Instantiate a new tokenprovider with a 30 seconds "
" time window "
tp := TOTP createWithSecret: key StepSeconds: 30.
" Calculates a new one time password which "
" changes every #StepSeconds seconds "
token := tp calculateOneTimePassword.
" Validate a token "
valid := TOTP verifyOneTimePassword: token Secret: key.

The larger the StepSeconds parameter the longer the generated tokens won’t change and the greater the time difference between client and server can be. The algorithm uses UTC for client and server times. 30 Seconds time step means that a new token is generated every 30 seconds and that a token is considered valid 30 seconds before and 30 seconds after the point in time it was created.

So change your Google account today and use Pharo to calculate the tokens.