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Making a $3 SRF04 Ultrasonic Sensor Act Like a $55 SRF08
12/19/2013

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Max The Magnificent
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What you didn't say...
Max The Magnificent   12/19/2013 1:44:31 PM
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Hi Duane -- what you didn't mention was that we first started bouncing the idea of this sensor board around one Friday afternoon -- when I talked to you the next day (Saturday afternoon) you'd already designed the board and sent a panel off to be fabricated -- you completely blew me away with this. Did you say you use Eagle PCB for these projects?

Duane Benson
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Re: What you didn't say...
Duane Benson   12/19/2013 1:54:46 PM
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Max - I did use Eagle. I currently use the free version. It's limited to two layers and approximately 3" x 4" in board space. It's also limited to non-commercial use. It's a great low-cost way to start designing PCBs. If I ever start to sell any of my creations, I'll need to upgrade to a commercial licence.

Max The Magnificent
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Re: What you didn't say...
Max The Magnificent   12/19/2013 3:01:46 PM
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@Duane: If I ever start to sell any of my creations, I'll need to upgrade to a commercial licence.

That means that so long as you are giving your creations away to me for free, you are OK ... I don't see a downside here LOL

Max The Magnificent
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What?
Max The Magnificent   12/19/2013 3:54:43 PM
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@Duane: In your blog, when talking about th efirst image of the SRF08, you say "The small part, between the two, near the top, is a CdS light-controlled resistor."

What is this used/required for?

Max The Magnificent
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Temperature, Humidity, and Pressure
Max The Magnificent   12/19/2013 3:57:45 PM
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@Duane: I've been told that the accuracy of untrasonic distance measurement readings is a function of temperature, humidity, and atmospheric pressure.

This is probably overkill, but since I'm intending on making my robot a veritable cornucopia of sensors, I'm planning on (a) adding these and (b) seeing how the untrasonic readings varies under different conditions.

a) Are you doing this for your robot?

b) Do you have any advice with regard to these sensors?

Duane Benson
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Re: What?
Duane Benson   12/19/2013 5:29:19 PM
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Max - re CdS cell.

It's just for measuring ambient light. One of the I2C calls returns the value. I might end up squeezing one into my board at some point, but until then, that's one feature it will be missing.

As far as adding temperature, pressure and humidity go, I'd like to have sensors for those environmental factors too.

David Ashton
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SR-04 modules
David Ashton   12/20/2013 12:41:07 AM
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Very nice work Duane.   I was curious about the modules and managed to find a data sheet on the SR-04 here.  They do have some electronics on-board - from the photos they look like they might be just the US devices only on the board.

I have a couple of boxes of US TXs and Rxs - just the bare transducers.  I'd thought of making something like this with them but for $3 it's just not worth it....

 

Max The Magnificent
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Re: SR-04 modules
Max The Magnificent   12/20/2013 11:19:30 AM
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@David: I was curious about the modules and managed to find a data sheet on the SR-04 here.  They do have some electronics on-board...

I think the on-board electronics on the '04 are just for pulse-shaping/controlling the out-going "ping" and detecting/registering/noise-filtering the incoming response...

Max The Magnificent
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Re: What?
Max The Magnificent   12/20/2013 11:23:21 AM
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@Duane: It's just for measuring ambient light. One of the I2C calls returns the value.

My knee-jerk reaction was that someone just happened to throw one on because they had it lying around ... after which it became part of the design.

But then I thought that they may have thought of using the sensor to detect someone coming into a room and activating the room's lights -- in which case they could use the ambient light level to decide whether or not to activate the main lights.

Duane Benson
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Re: What?
Duane Benson   12/20/2013 11:49:49 AM
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Max - I'm not sure what the purpose was. The original documentation just says: "The SRF08 can be used as a light sensor." That type of sensor really isn't senstive enough to detect someone coming into a room,

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