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ltj

Member since Feb 2014 • Last active May 2014
  • 1 conversations
  • 15 comments

Most recent activity

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  • in General
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    Both supplies, USB + led, has it's own ground. These must be tied together for the circuit to function. The pin strip is connected to the led supply ground, so the yellow wire simply connects the ground of the Espruino to the ground of the led supply.

    I will look at Arduino tutorials.....

    ...and don't hesitate to keep asking questions here :)

  • in General
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    Power to the rgb led comes from another power source not in the picture (could still be sitting in the breadboard power strip with the black wire). In this case, with just one rgb led, vbat could be used as well. The main point is you don't source power from the GPIO pins.

    Just to be clear: led power goes to the common-anode terminal (black wire), the cathode of the r,g and b leds (r/g/b wires) is connected to the drain of each mosfet. All mosfet sources are connected to ground. The espruino drives the mosfet gates. I can recommend the many tutorials on the same topic for Arduino. The exact same principles apply.

  • in General
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    @DrAzzy, if no load is on the 12V output you can see some nasty spikes on the 5V supply. I have observed this behavior myself, but others have also reported this like Paul Stoffregen at PJRC. It might be universal in the sense that the PSU design is pretty standard - they must provide the bulk of the power at 12V. However I have not seen it go past 9-10V so if your regulator/device can cope with this, you might never notice :)

  • in General
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    I second @DrAzzy, though I would not recommend an old computer PSU (ATX). The low voltage supply, 5V, is not stable when no current is drawn from the 12V output. For stand-alone operation using mains, a phone charger would be the best option - it's 5V, commonly ~1A these days and compact/efficient due to a switching topology. The Espruino power setup is also documented here.

    @ChrisB, using the bat_in or usb_vbus, vbat will be protected by a 1A fuse so no matter the input voltage you will be allowed to draw more than <1A on vbat. If you choose to power the Espruino directly on vbat be warned that you do not get reverse polarity protection nor a fuse to protect you peripherals and the board. You can still switch high currents safely with the Espruino using mosfets or relays though.

    If you have peripherals connected that runs on higher voltages, yes, then you would need more than one power supply. Alternatively you can use one mains PSU that delivers 24V DC and then use voltage regulators to give you 12V and 5V as well from the same source. No matter what, all your devices must share a common ground to function properly.

  • in General
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    Just thinking aloud here....it's most likely much better to implement this in a library and have the event loop reset the counter?

  • in General
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    Absolutely. According to the datasheet the STM32F103x family of mcu's have 2 watchdog timers. You control them via registers, and you can write register data using the poke8/16/32 functions. Do be careful however. The watchdog counter needs to be reset at your discretion. ie. if you have a program that just sits and wait for an external interrupt (say, a PIR motion sensor), and nothing happens for a while. Then you need to make sure that you counter reset takes place in a setInterval().

    You can see all the register documentaion and much more in the ST reference manual found here.

  • in Interfacing
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    You should not use a resistor like the thermistor tutorial suggests. Instead you connect the output pin (white on the Atlas device) on the MCP9701 directly to an ADC pin on the Espruino. The voltage you read is proportional to the temperature. Use the calculations described in the atlas datasheet to get the actual temperature. Just remember that Espruino analogRead returns a resolution-independent number between 0 and 1, and the Aref voltage is 3.3V.

  • in General
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    @Samarthwiz, no the A, B C refers to the GPIO ports (groups of i/o pins if you like) on the STM32F103xx chip. Microcontroller pins usually have more than one function, ie. can be both analog or digital in the Arduino sense. You can see what each pin can be used for in the reference: Espruino Board

  • in General
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    Regarding HTTPS, doing ssl/tsl libs on a small mcu (like stm32 mid-level) would definitely not be feasible imho. One of the problems being the shear no. standards that need to be implemented as well as the performance of software AES. Some mcu's, like the Atmel AT32UC3A3256S, does sport a hefty AES crypto module that could come in handy here though.

    @Gordon, super excited to hear about the WIZnet support.

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