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ryanm
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Posted: 11 October 2018 at 9:50am | IP Logged Quote ryanm

Had a few suggestions, but they all run at 3.3V. Haven't managed to find a cheap sealed ultrasonic transducer that runs at 3.3V. Maxbotix ones do, but they're around $150.


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Volhout
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Posted: 11 October 2018 at 7:34pm | IP Logged Quote Volhout

Hi,

This is typically something I would do in a PICAXE. The PICAXE microcontrollers have a sh*tload of sleep and low power commands build in that actually work.
The ultrasonic range finder can be implemented using pulseout and pulsein commands (search picaxe forum).

Regards,

Volhout

Edited by Volhout on 11 October 2018 at 7:35pm


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Timbergetter
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Posted: 11 October 2018 at 10:38pm | IP Logged Quote Timbergetter



Grogster wrote:
CaptainBoing wrote:
Which MOSFET did you end up using Grogs?


I used a DMP2305, which is SOT-23, and has an RDS of 90 milli-ohms at -2.5v
Vdss of -20v, Vgss of +/-8v, I=-4.2A. I helped that along with an FMMT493 NPN transistor in SOT-23.


Grogster, I found the above image on another thread and I guess it is the circuit you are referring to. You desribe it further in that thread with the following:
"This was what I have been using up until now, but it requires four extra SMD parts.
It is a high-side switch for just about anything with a common-ground.
I used 1k for R7, 100k as the R6, the NPN I used was an FMMT493 in SOT-23 flavour, and the MOSFET I used was a DMP2305 also in SOT-23. "
Many thanks for all your info.
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Timbergetter
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Posted: 11 October 2018 at 10:43pm | IP Logged Quote Timbergetter

Volhout wrote:

This is typically something I would do in a PICAXE. The PICAXE microcontrollers have a sh*tload of sleep and low power commands build in that actually work.


I've not had any contact with the PICAXE but I'll certainly look at it if I hit an impasse with Arduino.
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ryanm
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Posted: 11 October 2018 at 11:03pm | IP Logged Quote ryanm

I wouldn't be too concerned with what chip framework you go with. There are at least half a dozen common ones out there that could do the job no worries, just use what's familiar to you. Getting the micro to sleep is easy with freely available libraries. It's managing the ultrasonic and radio that will eat up your battery.
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lizby
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Posted: 11 October 2018 at 11:20pm | IP Logged Quote lizby

Timbergetter wrote:
Volhout wrote:

This is typically something I would do in a PICAXE. The PICAXE microcontrollers have a sh*tload of sleep and low power commands build in that actually work.


I've not had any contact with the PICAXE but I'll certainly look at it if I hit an impasse with Arduino.


Plus 1 for getting the picaxe to operate at very low power. 10 years and 10 months ago I built a picaxe circuit to test very low power consumption, and powered it with 3 not-new AAs. It doesn't do anything except blink a barely-visible LED once every 7 seconds. It's still running: https://picaxeforum.co.uk/threads/low-power-battery-backup-reference-design.8353/

Agree that the real cost is going to be powering the HC-12. I intend to find out about that soon with a similar temperature-measuring task. I will be happy if I can get 6 months out of 3-AAs, waking up about once an hour and transmitting only if there is a nominal temperature change of at least 1 degree (16 16ths of a degree with a DS18B20).


Edited by lizby on 11 October 2018 at 11:25pm
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Timbergetter
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Posted: 12 October 2018 at 9:42am | IP Logged Quote Timbergetter

Grogster, I was wondering if you could tell us a source for DMP2305 that doesn’t involve outrageous shipping costs to Aus? Mouser seem to charge a min of US$24 for that service.
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disco4now
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Posted: 12 October 2018 at 10:25am | IP Logged Quote disco4now

RS Components have free shipping. You get 100 for $13.50

rs components
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Grogster
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Posted: 12 October 2018 at 10:46am | IP Logged Quote Grogster

I got mine from Element-14 at the time:

Link.

74c each in NZ money, and freight is free if you buy $50 or so worth of parts.
I usually combine my orders so that when I make an order from Element-14, it is at least $50 so I can get the free courier. Otherwise, it is $15 I think.

EDIT: Disco's link is a better price. I'd buy them from there, but you might not want 100 of them.

These MOSFET's have a maximum Vgs of 8v, so you can't connect the arrangement from the photo above to more then 8v or you will probably destroy the MOSFET. As the HC12 only needs 5v, they are perfect for that. Just don't go putting 12v on it like it shows in the diagram above!

Edited by Grogster on 12 October 2018 at 10:51am


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Timbergetter
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Posted: 12 October 2018 at 11:07am | IP Logged Quote Timbergetter

Thanks disco4now. 100 units on its way now. That should keep me out of trouble for a while!
Thanks Grogster for the Element-14 tip.
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