Motor shield and cc3000 breakout shield..

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mkkb
 
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Re: Motor shield and cc3000 breakout shield..

Post by mkkb »

Ok, so do you have another solution in mind? If i find a multiplexer that can handle high voltages which will switch the input voltage between the different sensors maybe? Do you have something like that in the store?

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adafruit_support_bill
 
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Re: Motor shield and cc3000 breakout shield..

Post by adafruit_support_bill »

Let me check with one of our analog experts and see if he has any recommendations.

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mkkb
 
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Re: Motor shield and cc3000 breakout shield..

Post by mkkb »

Thx alot:) I also found this part: http://www.intersil.com/content/dam/Int ... -53%20.pdf. Maybe it will do? (if u saw my post before i edited i meant this part;)

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Re: Motor shield and cc3000 breakout shield..

Post by adafruit_support_mike »

Looking at the datasheet, that multiplexer has an ON resistance of about 125 ohms from a 5v supply. That's okay for low-current signals, but I wouldn't use it to control power.

I agree with Bill that you want to avoid low-side switching for sensor power. GND is the reference voltage for most measurements, so any resistance in the GND connection between a sensor and the device that reads it invites trouble.

High-side switching is okay though. Even if there's an offset voltage, you can measure it relative to the shared GND reference.

Normally I'd suggest a relay for any power switching.. it's hard to beat direct metal contact for on-resistance and an air gap for off-resistance. Those tend to be power hungry though. Even reed relays want around 10mA to hold the connection closed.

Since you want to conserve power, I'd suggest using P-mosfets. Most of the ones you can get these days have an on-resistance in the milliohm range when you put 5v between the gate and source, and if you're willing to work with SMT components they only cost 10-20c each. Through-hole versions cost more because there's more metal and plastic in the package, and the mosfets inside tend to be rated for higher current levels. There's no rule that says you have to run them at their limit though, and their on-resistance tends to be really low.

With P-mosfets controlling power, and the Intersil multiplexer controlling the connections between the sensors and the Arduino, you should be able to drop the current going to unused sensors to a few picoamps. To get lower than that, you have to worry about things like the conductance of humidity in the air, so "as close to zero as reasonably possible".

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mkkb
 
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Re: Motor shield and cc3000 breakout shield..

Post by mkkb »

Ok, thx for an informative answer:) So if i combine some p-mosfets (like this one: http://www.jameco.com/Jameco/Products/P ... 222457.pdf) with a 74hc595 shift register that would be a good solution for power management?

Anyway im very new to this and right now i just wanna get my project going, so at first im just gonna stick with the ISL84051. Before i read your post i made the following setup were everything except the motorshield and motors are controlled by the muxes, one for 5v and one for Vin=12V (i removed the motors just to save picture space:). Would this work, or which parts should i disconnect from the muxes and couple directly to the arduino (or later control with a p-mos/shift-reg device)?

Thx again:)
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Re: Motor shield and cc3000 breakout shield..

Post by adafruit_support_mike »

According to the datasheet you posted, the ISL84051 has a maximum current rating of +/-30mA, and can survive pulsed current up to 100mA if the pulses are only 1ms long and you only have one pulse per 10ms (10% duty cycle).

How much current do your load cells need?

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mkkb
 
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Re: Motor shield and cc3000 breakout shield..

Post by mkkb »

I figured out earlier that the load cells gives an max output of 6mV when powerd by 12v from the arduino, the data sheet says it has Zi=1115ohm and Zo=1000ohm, so it needs around 6 microAmpere? And the ina125 amplifier needs 0,46 mAmpere at the same time.

Another question: I understand that you do not sell extra tubing to the 12v motor peristalic pump, correct?

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Re: Motor shield and cc3000 breakout shield..

Post by adafruit_support_mike »

Load cell datasheets are hard to read until you get used to them, but the current consumption depends on the input impedance and supply voltage. In this case, 12v/1115-ohms translate to a current of about 11mA.

The 6mV/V output figure tells you what to expect when the cell is loaded at its maximum weight. The output is proportional to the input, so for every volt at the supply, you can expect 6mV at the output. For a 12v supply, you should see about 72mV between the output terminals when the cell is fully loaded. If your supply voltage was 10v, you'd only expect 60mV of difference at the output.

Since the output depends on the supply voltage, you want as few additional errors in that path as possible.

WRT peristaltic pump tubing, we don't sell that separately, but you can get it from places like McMaster-Carr.

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mkkb
 
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Re: Motor shield and cc3000 breakout shield..

Post by mkkb »

Hi again. I have an new iusse regarding the soil sensor (http://www.adafruit.com/products/1298#d ... ion-anchor) i bought, which i wanna use it to measure the soil humidity to a plant. And my problem is that when using relative dry earth, the driest i can get without using external heat, i get 100% humidity readings when i bury the sensor. So is there a way to increase or shift the measuring range somehow?

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Re: Motor shield and cc3000 breakout shield..

Post by adafruit_support_mike »

Just posted a message about that over here: http://forums.adafruit.com/viewtopic.ph ... 04#p281704

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mkkb
 
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Re: Motor shield and cc3000 breakout shield..

Post by mkkb »

Hi again:)

I finally bought me some p-mosfets (http://radioremont.com/datasheet/APM4953.pdf) which i will controll with the intersil 84051 multiplexer (http://www.intersil.com/content/dam/Int ... -53%20.pdf) to lower power consumption. And i just wanna do a simple setup controlling 5V supply from the arduino and maybe 9 or 12V from the motorshield to control multiple motors. And im just wondering if there is something i must concider or any pitfalls to avoid before i start soldering? Should i use some capasitators anywhere or something? With the motorshield i will of course turn off the power before i switch with the mux. Remeber im a newbie and no expert:)

Thx for any help!
BR Kris

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adafruit_support_mike
 
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Re: Motor shield and cc3000 breakout shield..

Post by adafruit_support_mike »

IIRC, you were going to use the Intersil multiplexer to control the connections between the sensor data lines and the Arduino, and the P-mosfets to control power to the sensors.

If that's the case, you have all the parts you need. You'll need four Arduino pins to control the ISL84051: one for the signal input and three to set the address. You'll need one Arduino pin to control each P-mosfet, with HIGH signals turning the power off and LOW signals turning the power on.

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mkkb
 
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Re: Motor shield and cc3000 breakout shield..

Post by mkkb »

So how do i tell from the datasheet that the mosfet is active low? So i can't use the MUX to control the mosfets then to turn "on power" to one sensor/motor at the time? My initial idea was to controll all the mosfet with the multiplexer (if im unclear in what i want i can post a fritz pic later).

Thx for fast reply by the way:)

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Re: Motor shield and cc3000 breakout shield..

Post by adafruit_support_mike »

mkkb wrote:So how do i tell from the datasheet that the mosfet is active low?
All P-mosfets are active-low. It shows up in the datasheet as a negative Vgs value:
Features
-30V/-4.9A,
RDS(on)=53mΩ(typ.)@VGS=-10V
RDS(on)=53mΩ(typ.)@VGS=-4.5V
mkkb wrote:So i can't use the MUX to control the mosfets then to turn "on power" to one sensor/motor at the time?
You can do that too.. just connect the 84051's COM pin to GND and all the other inputs to the gates of the mosfets.

Since the 84051 can only pull the gates LOW (turning them on), you'll need pull-up resistors to turn them off. Connect a 10k to each gate so it's HIGH until the 84051 pulls it LOW.

If you want, you can use two 84051s: one for the mosfets, one for the sensor data lines. The same address pins will work for both switches.

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mkkb
 
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Re: Motor shield and cc3000 breakout shield..

Post by mkkb »

Thx, i think i understand what you mean. I made this simple sketch to show i interpreted your reply. So here I have a setup with to sensors, and the sensor to the right is now active via the channel No0 on the mux, correct?
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MuxMosSetup.png
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