Author Topic: Review of a current pcb design/improvements  (Read 2048 times)

silentone

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Review of a current pcb design/improvements
« on: July 01, 2018, 08:33:50 PM »
Hi there,

I've been working with the RFM69 radios with a DHT22 sensor to some mild success, wanting to achieve some wireless temperature sensors but am finding battery life to be an issue. The design has implemented the LTC3525ESC6-3.3 to my design but not finding the life fantastic (2-3 months on 2x AA batteries) and not sure what else to try.

I'm looking for someone who can do a full review of my fritzing design/arduino code and getting a redesign done (if required) and better antenna mounting options.

Currently its a

  • ATMEGA328P running at 8mhz
  • DHT22 (which i'm willing to change for another humidity/temp sensor)
  • RFM69HCW 433mhz with standard wire antenna
  • LTC3525 Booster
[li]6 DIP switches
[/li][/list]


LukaQ

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Re: Review of a current pcb design/improvements
« Reply #1 on: July 02, 2018, 05:39:39 AM »
what is your current draw, duty cycle?

Felix

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Re: Review of a current pcb design/improvements
« Reply #2 on: July 02, 2018, 10:20:52 AM »
Why the extra complexity and BOM cost of the booster when you have 2xAA power source?
It's been shown that at 8mhz you can run down to 2V without any issues (even below that). Unless you're trying to avoid any "overclocking" maybe?

perky

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Re: Review of a current pcb design/improvements
« Reply #3 on: July 02, 2018, 02:12:48 PM »
The OP is using a DHT22 sensor, it requires at least 3.3V. If the booster is only turned on when accessing that (with some voltage translation) that would reduce the average current. I'd look at a different booster type though, that LTC has 400mA peak inductor current which might cause voltage drops with depleted batteries due to increased internal resistance. It might be better to boost to 4.5V or so with a fixed on time or inrush limiting booster circuit and regulate that to 3.3V with a LDO. Or find a sensor that works down to 2V.

Mark.

silentone

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Re: Review of a current pcb design/improvements
« Reply #4 on: July 02, 2018, 06:09:50 PM »
Why the extra complexity and BOM cost of the booster when you have 2xAA power source?
It's been shown that at 8mhz you can run down to 2V without any issues (even below that). Unless you're trying to avoid any "overclocking" maybe?

It was a kind of throw the kitchen sink at it to make it work after doing reading, i've been thrown in the deep end with this project - i'm a software engineer and don't develop with hardware, i've done my best but am now needing someone who knows what they're doing.

The OP is using a DHT22 sensor, it requires at least 3.3V. If the booster is only turned on when accessing that (with some voltage translation) that would reduce the average current. I'd look at a different booster type though, that LTC has 400mA peak inductor current which might cause voltage drops with depleted batteries due to increased internal resistance. It might be better to boost to 4.5V or so with a fixed on time or inrush limiting booster circuit and regulate that to 3.3V with a LDO. Or find a sensor that works down to 2V.

Mark.

The booster is supplying power to the whole circuit, and it turns the DHT22 on/off as it needs it.

I have to produce a sensor that can last at least a year on 2x AA batteries, using the RFM69HCW chip that sends temperature/humidity back every 2-3 minutes.

Is this something either of you are interested in quoting/working with me to produce something?

Felix

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Re: Review of a current pcb design/improvements
« Reply #5 on: July 03, 2018, 09:55:56 AM »
silentone,
See my email response to your message with suggestions and possible simplification to this project.
Essentially I dont think you need a booster at all. You could also use a BME280 sensor (available on WeatherShield) with a Moteino and power it from a small solar cell if outside or by a window, or even from a tiny lipo cell and it will last more than 2 years.

silentone

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Re: Review of a current pcb design/improvements
« Reply #6 on: July 03, 2018, 05:02:41 PM »
Thanks everyone, i'm in discussion with getting the work done.. exciting! :)