Power saving for gps mdule using esp8266

Hello guys; am working on a project for tracking for a certain period during day time and upload to server at night time. the problem i have is i am using deep sleep on the nodemcu module to deep sleep for two minutes and wake up and read the gps + save on sdcard in the space of 30 seconds. what i notice is that during the deep sleep the gps module is still on probably also the sd card (not sure).

i think the reason is because the gps and sd card module vcc pin is connected to the nodemcu 3v pin. and if i use a digital pin instead to give a high or low input to the vcc pin of both gps and sd card i will be able to turn both modules off but i want to know why it is not going off when i give the deep sleep and moreover i dont have anymore pin available.

thanks

Deep sleep will not turn off the 3.3v. Check if the gps module has a standby mode. You can’t power the module directly via a esp8266 gpio pin because the current will be too high but you could try a transistor or mosfet.

Putting the esp8266 into deep sleep does not put all other attached devices or modules into deep sleep as well. This is the case for proper Arduinos too.

Each attached device will have its own method of being put into a low current mode and on some devices its probably not possible, like with SD cards for instance.

Most GPS can be used for short periods in 'hot fix' mode, whereby the power is removed and when its connected again it aquires a new fix in a couple of seconds. However for most all GPS modules I have seen this 'hot fix' ability fails after a couple of weeks so that every time the GPS is turned back on its running from cold and takes 45 seconds or so to aquire a fix, this uses a great deal of power.

For an SD card you need to remove the VCC connection to save power.

And before you get too far down the design route and work out that you cannot get the power down low enough, what is the battery type and life that is acceptable for the project ?

i am using ultimate gps module. it has enable pin which can be used to turn the gps on or off and also found that the gps has a 64k memory which is been saved on every 15 seconds will last for 16hours.

also found this which says that at least 25mAh is still been drawn from the battery when the nodemcu even in deep-sleep mode.link

srnet: And before you get too far down the design route and work out that you cannot get the power down low enough, what is the battery type and life that is acceptable for the project ?

i want all the device with a battery of 2400mAh to run for at least 3 days before recharge. more over am thinking i will have to make my own pcb using the ic chip of the esp only since it will eliminate the 25mAh been drawn when in sleep mode. i found the SparkFun ESP8266 Thing link: https://www.amazon.com/dp/B00YUU4AMK?tag=openhomeautomation-20

more expensive than normal nodemcu.

right now am going to try the "hot-start" of the gps and see how long it takes to get a fix after 2 minutes of sleep

Azeez_Jimoh: right now am going to try the "hot-start" of the gps and see how long it takes to get a fix after 2 minutes of sleep

The initial hot-start might only take a few seconds, but the average for that GPS over 24 hours will be around 11 seconds.