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I am currently working on a project where I was looking for a microcontroller that is capable of BLE (Bluetooth Low Energy) which determines a servo's position. Using an Arduino the project works well on a breadboard.

To have a better design of the project and enhance the energy efficiency (I need to use batteries and no breadboard) the Adafruit Trinket was recommended as once covered within this forum (For a 'customized' arduino consuming less energy making use of Attiny85 vs PCB Fabrication?). As I read I need to use the Adafruit Trinket Pro since the normal trinket with an attiny85 microcontroller will not enable me to attach a BLE module.

Researching on Trinket Pro 5V I found out that the onboard 5V regulator can provide only 150mA output and not 800mA unlike an Arduino Uno. Therefore I cannot attach the servo(250mAh/4,8V/6V) on the Trinket.

Now I was planning to make use of ONE battery box (6V) and attach it on the Pro Trinket, BLE Module and Servo. I don't see any other good solution given the requirement that I need to use only one 6V battery box. I am aware of the risk that the if the Servo uses too much current the device will not work anymore due to the lack of energy. However I will make use of Sleep and interrupt functions to increase the lifetime of the device.

Given the fact that I require a collaboration of a microcontroller, a BLE module and a servo motor, is there a way to use them together in a beneficial/recommendable way?? As of now I consider to attach all of them on an Adafruit Trinket Pro. However I guess I am thinking too naively; especially considering the battery requirement.

There was a similar question but I cannout extract a useful answer for me from the answers provided there (Using adafruit Flora or Adafruit Trinket + MPU-6050 3-Axis Gyroscope + nRF24L01+ together)

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Sathees
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  • You can't find useful answers at the linked question because it wasn't a very good question. Same here. You can't get blood from a stone, and you seem to know that. – Scott Seidman Aug 11 '15 at 22:21
  • @Scott see my updated qustion...I hope to be more clear on my question nw – Sathees Aug 12 '15 at 00:02
  • The ATtiny85 doesn't have a hardware USART. I hope you're ready for a little bit of pain in getting this working... – Ignacio Vazquez-Abrams Aug 12 '15 at 00:04
  • Don't mean to be rude, but *PLEASE* expand your acronyms at least once in your question. I didn't known what BLE was until I read the comments. – Dwayne Reid Aug 12 '15 at 01:35
  • @IgnacioVazquez-Abrams the Adafruit trinket Pro contains an atmega 328 microcontroller and hence should have USART....you are definitely right that the normal Adafruit Trinket (attiny85) has no USART..therefore attaching BLE module would have been an issue with that one... – Sathees Aug 12 '15 at 07:30
  • Ah, I completely missed the "Pro" part. That will teach me to skim (...or will it?). – Ignacio Vazquez-Abrams Aug 12 '15 at 07:36

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The Atmega328P can actually use a supply of up to 5.5V, so using a silicon rectifier to reduce the 6V and a bulk capacitor (after the diode) to help with brownouts will work, and the servo will be supplied directly off the 6V battery. If your BLE module needs 3.3V then you will have to use a separate regulator for that.

Ignacio Vazquez-Abrams
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  • Thanks a lot...do you see any concern in this construction? – Sathees Aug 12 '15 at 07:42
  • Make sure you don't use a Schottky diode by accident, since its forward voltage is too low for this. – Ignacio Vazquez-Abrams Aug 12 '15 at 07:43
  • Ok. Good to know. Is it ok to use a voltage regulator to make sure that the servo only works with 4,8V instead of 6V. Is this an advantageous approach? – Sathees Aug 12 '15 at 07:45
  • Eh, if the servo works with 6V then it will reduce complexity and part count to connect it directly. Plus, the faster it moves, the shorter the brownouts will last. – Ignacio Vazquez-Abrams Aug 12 '15 at 07:47
  • so u mean it is preferable to connect it directly to a 6V battery box and let it work that way? – Sathees Aug 12 '15 at 07:49
  • That is exactly what I mean. – Ignacio Vazquez-Abrams Aug 12 '15 at 07:50
  • I just came to know that there is also an Adafruit Trinket PRO 3.3 V so in that case I will need only one regulator and capacitor from the battery box to the trinket and frm the trinket 3V output pin I can attach a BLE withot any regulator – Sathees Aug 12 '15 at 13:18
  • In the answer u said a bulk capacitor after the voltage regulator....which value do u have in mind? – Sathees Aug 13 '15 at 16:38
  • I'd start with a 1000uF 10V aluminum electrolytic, with power saving being used in the MCU of course. You may also need to tweak or disable entirely the BOD of the '328P. Note that you may require a diode regardless depending on how deep the brownout is; some regulators do not like being reverse biased. – Ignacio Vazquez-Abrams Aug 13 '15 at 16:45
  • did you recommend to disable the BOD in order to have the chance that many parts of the atmega remain working even at small voltage level in case of a BOD? I was planning to use a bucket converter LM2594..should be fine right? – Sathees Aug 13 '15 at 19:45
  • Disabling the BOD is a good idea to start, as is using a lower clock rate (via prescaler is fine) both to survive lower voltages and to use less power when running. – Ignacio Vazquez-Abrams Aug 13 '15 at 20:31
  • The diode is a bad idea as the "6v" battery box will be more like 6.4 volts with fresh cells. – Chris Stratton Jan 18 '17 at 14:50
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I am currently working on a project where I was looking for a microcontroller that is capable of BLE which determines a servo's position.

Cypress has microcontroller+BLE solution. Have a look, PRoC™ BLE (Bluetooth Smart)

Here is a link to datasheets

Mahendra Gunawardena
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Duresh
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  • Thanks for your answer... On the link provided I cannot find any device ehere a microcontroler and a BLE module are attached together. I just had a look on the CYBL10X7X Family Datasheet... – Sathees Aug 12 '15 at 07:47
  • There are two types PSoC and PRoC. Both are programmable and both has BLE on chip. Their IDE has graphical interface to configure the processor. these are the datasheets. http://www.cypress.com/file/137466/download – Duresh Aug 13 '15 at 09:11