![]() You can implement double buffering, if you are clever at programming. ![]() Hopefully that is how you are currently doing it! Still have the time delays writing a 512 byte buffer to the SD card. (most buck converters make a lot of electrical noise) Trying to get 12 to 18 bits of data in a noisy environment can be a challenge. You may find you don't need a buck converter. Most devices work down to 2.2 volts or so. ![]() I've not calculated out the memory you require so this is just a suggestion. This will require you to "decode" the data to read but will be much faster.ĭo you need an SD card or could you get by with EEPROM(s). I would write the data in binary (as opposed to ASCII). From then on I would only write the data, knowing the sample rate you know the time between data entries. I would use a library that does only alpha/numeric and no graphics.įor time logging I would initiate the program writing the full time and date. Most/all? displays remain at whatever was displayed until you update, and you can usually update only parts of the display. ![]() I would use an ESP32, mostly due to the 3.3v operation which matches the SD voltage levels. I don't know much about SD power requirements so I can't help there. via a P-Mosfet in series with the power supply to the SD card : taking into account the requirements of data acquisition load), is it worth considering such additional hardware ?Ĥ.3 : For the temporary display (320X240 ILI9341 that I have), I am of course considering such power control (via a P_mosfet) for inactivationg the display consumption when the display is not used : but is the arduino library (ILI9341_t3) compatible with such supply power manipulation, for putting to sleep/awakening without problem ?ĥ : is it worth and appropriate to consider adding a memory chip (spi interface) to increase the buffer size for dumping the data in larger chunks onto the SD card ?Ħ : how to avoid ecg data loss when the real-time clock will be accessed (say every nearly full buffer, and complementing the data in the buffer with the date/time before dumping it to the SD card ?ħ : should I look into a real-time OS ? For the present project as described, Is it worh the pain and the steep learning curve ?ħ.1: in such case (RT-OS), are there worked-out solution for the « fast » SD card data logging (speed compatible with the requirements of the present project? Is there an identified current winner in term of popular SD brand/model reference) ?Ĥ.2 : I have seen some posts where the power to the SD card is lowered (e.g. I want a 3 volts system (and not a 5 volts one), in order to use either a lithium battery or LiFePo4 battery with a appropriate buck regulator delivering 3V to the whole system.ġ : Would an esp32 (or an arduino nano?) do the job (esp32 with wifi/bluetooth inactivated to save power) ? What would be good arduino-IDE compatible alternate choices ?Ģ : is the requirement ‘without interrupting the SD card logging ‘ realistic if the display is activated ?ģ : Is the sdfat library an appropriate choice ?Ĥ.1 : I understand from older posts (circa 2015) that the the power consumption of various flavors of SD card varies wildly and that I should stay away if possible from « (circa 2015) high capacity » SD card However looking for example at AliExpress, the lowest sd card capacity I could find is already 8Gb : what is the current situation of various power consumption with 8 Gb sd cards ? should I beware of the class of the SD card ? I want to interface concurrently an ecg chip such as the Max30003 (spi interface), an sd card logger (spi interface), and a real-time clock (I2c interface) and possibly upon temporary user choice activate a 240X320 display (spi interface), to pick a view of the incoming data, without interrupting the SD card logging It appears that the SdFat with its 512 byte buffer might be a possible solution. Looking at various sources of info with search key words such as ‘fast portable sd card data logging arduino’ The goal is to provide me with a home-made portable ecg recording system. I am at the stage of determining the necessary hardware and software, that would allow a uninterrupted low power (24h or 48h portable) 12 to 18bits data logging at 200 Hz to a SD card. * * Created by ArduinoGetStarted.This post is about both hardware and the related software (is this "hardware" section appropriate ?)
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