I would like to have You support on my following project:
Goal: Make a shield for sensors in the Greenhouse.
(The same PCB shield can be used for NODE & GATEWAY as well. Only different configuration required.)
Board: Arduino MEGA Issue: The board can take max. 200 mA and deliver max. 40 mA (on one pin)
The sensors and transmission circuits are taking much more 100-300 mA approx., depending on sensor reading & transmitting phase to the Gateway.
The reading of the sensors required only after 10 minutes and only for max. 1 minute.
So to save energy and extend the operation time of the battery (power bank)
I would like to switch ON the sensors before reading and switch OFF after reading and the communication done with the gateway.
I come up with the following sketch. I would like to ask, before damaging the sensors or the board: Can it work?
My problem is the load is changing in the 1 minute.
Hi,
The schematics seem to be right in the electronic side of the project. I would suggest you consider checking some of these issues:
If you're using some standard USB kind of powerbanks, most of them turn off when the power drain is lower than a set value, check and try it before deploying or you'll end up with a power loss in your board.
Some of the sensors you've mentioned have a delay from power up to full function and reliable data aquisition and transmition. I've experienced the delays with the DHT22 and the ESP8266 myself. That will add for useless energy consuming while the sensors are booting.
Some of the sensors you mentioned must be configured in some way when you turn them on, and don't keep the configuration after being turned off, so you'll have to reconfigure them once and again when you periodically turn them on.
After all said in the previous points, maybe your project will benefit from a mixed energy management solution: for some sensors turning them on and off, for some of them putting them to sleep or in a low energy consumption mode. For example, some displays have a power-in pin for the logic, another pin for backlighting... keep the logic always on, the lighting might be turned on and off.
Last but not least: if you're in doubt ditch the 10KmA power bank, 20KmA and 30KmA are available at the same store... and those are not double or triple price of the first one.
You may have a problem low side switching.
I would suggest high side switching and as pointed out, some sensors will need resetting each time you power them up.
Considering the stable power required on some sensors, I would recommend you power this with a SEPIC (Buck/Boost) converter. You can set its output to 5V or as I do set it at 8 and power through the Vin. The SEPIC converter will eliminate the voltage swing you will see from discharged to fully charged modes of operation and everything in between.
Thank You for Your feedback!
I was afraid from something like this.
Instead of transistor & resistor, shall I use signal relay (coil take 30 mA < 40 mA)
like: HOGFA HFD4/5?
I would use a an SSR, Solid State Relay switching the high side of the load. They burn a lot less of energy. Still a risk tha the downpowered device will try to pu current through the logic signal kines.
What can I say, I use that one several times, it has always worked great for me. It showed up as $500 on your link, but the currency sign was blurry at best so that price had to be wrong. I get them from my china supplier, it takes a few weeks but they are much less.
The 4N25 is an old timer but it is a good part and it will serve you well.
[quote="steger, post:16, topic:1229844, full:true"]
Thanks a lot for Your prompt reply. The price is 499 Indian rupees (6 USD )
As I see in the comments SSR can be used as well, but I can find only such a relay, where DC controlling AC current.
I would highly appreciate if You can propose something modern solution, instead of my "old timer" collection
)