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Author Topic: Autonomous Vacuum Cleaner  (Read 9029 times)
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Atlanta
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1. What mosfet shall we use? Can you recommend the exact part no.? We will use 15v dc to "activate" this mosfet by the way.
One that handles the voltage and current, and can turn fully ON with the gate drive you have.  Cant recommend one without knowing all your sources and loads.  The MOSFET is activated by the presence of external power, are you supplying +15 V DC to the interface between docking base and robot?

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2. Will the switching of mosfet be fast enough that the arduino will not reset?
With the usual filtering and bypass capacitors on voltage regulators and Arduino it should not be a problem.  Add more capacitance if you have trouble.

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3. What diode shall we use? Is the common 1n4001 appropriate?
Common rectifier is OK if you dont exceed the ratings.  That one is good for up to 1 amp.  An even  better choice would be Shottkey diode which has lower forward voltage drop.


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4. We want the charger to be connected to the AC mains only when the robot is docking on the home base, can we use a relay to do this task?
Yes.  Or a mechanical switch.
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Makati, Philippines
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@ AltairLabs

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One that handles the voltage and current, and can turn fully ON with the gate drive you have.  Cant recommend one without knowing all your sources and loads.  The MOSFET is activated by the presence of external power, are you supplying +15 V DC to the interface between docking base and robot?
Yes. We will create a voltage regulator with output of fixed 15v dc, this way there is enough voltage for good line regulation of our switching regulators supplying the brain. What parameters of fet shall we watch out for?

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With the usual filtering and bypass capacitors on voltage regulators and Arduino it should not be a problem.  Add more capacitance if you have trouble.
Before or after the switching regulators? Before the IC, we will put 100uF/25v, after we will have 330uF/16v.

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Common rectifier is OK if you dont exceed the ratings.  That one is good for up to 1 amp.  An even  better choice would be Shottkey diode which has lower forward voltage drop.
Okay. So we will use 1n5820 (20v 3A).

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Yes.  Or a mechanical switch.
Do you reckon microswitch is better than relay for connecting AC?

Thanks. Will post partial schematic later. ^^
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What parameters of fet shall we watch out for?
One that handles the voltage and current, and can turn fully ON with the gate drive you have.

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Before the IC, we will put 100uF/25v, after we will have 330uF/16v.
sounds like enough, try it and see.

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So we will use 1n5820 (20v 3A).
good choice, assuming loads are under 3A.

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Do you reckon microswitch is better than relay for connecting AC?
cant say, as I dont know the purpose of this.  to turn off +15V when the dock is empty?  what will activate the microswitch or relay? can it be falsely activated?  is +15v easily accessible?  current limited? why does it matter?

Tell me if we have in mind a similar idea:

sorry it just makes more sense to me drawn this way.

Since your VEXT is so much above your battery voltage, the body diode of the FET might conduct, so I added a diode after the FET, too.  But since you have plenty of overhead voltage you no longer really need the FET, just a pair of diodes will be fine.

This version also shows advice from the various gods, such as the heavy loads need to be wired with their own "home run" to the single point ground.  The BRAIN is Arduino plus sensors, no heavy loads.  If your other servos are substantial loads they can have their own ground too.  This "star" ground ensures  the charger and brain dont get confused by IR drop from common ground current.

If you keep your grounds well controlled, there is little reason not to put +5V regulator direct to Arduino +5V per AWOL and smeezekitty.  You need to control grounding anyway to keep noise out of analog inputs and low voltage sensors.

For switching heavy loads use FET and include a few K of gate resistance.  That way any "ground bounce" can get dissipated harmlessly.  This might cause some ugly switching but you'd rather have it there than mixed in with your low level IO.

As the gods pointed out the Arduino battery monitor voltage will depend on loads.  Best to monitor voltage when heavy loads are idle.  You can test the battery under load, but you need to know the current and use different criteria for voltage vs charge.
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@ AltairLabs

Sorry, me being novice. But I am willing to read a lot. Really glad there are people like you.

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One that handles the voltage and current, and can turn fully ON with the gate drive you have.
By the way, I have not used MOSFET before, so I don't know what to choose. The LiPo battery will power the ArduinoMega (current consumption I cannot compute), 3 IR sensors (about 100mA max for the three), 2 servos (we checked a while ago, the consumption is about 250mA for the two), LCD (150mA including BKL), and vacuum pump (about 500mA max).  What FET do you think will handle this?

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cant say, as I dont know the purpose of this.  to turn off +15V when the dock is empty?  what will activate the microswitch or relay? can it be falsely activated?  is +15v easily accessible?  current limited? why does it matter?
I hope the image below will clarify what I am trying to say before. ^^

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sorry it just makes more sense to me drawn this way.
Don't be sorry. You are the one helping me. The fact that you drew that thing is a big help to teach in the first place.

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Since your VEXT is so much above your battery voltage, the body diode of the FET might conduct, so I added a diode after the FET, too.  But since you have plenty of overhead voltage you no longer really need the FET, just a pair of diodes will be fine.
I don't understand.

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This version also shows advice from the various gods, such as the heavy loads need to be wired with their own "home run" to the single point ground.  The BRAIN is Arduino plus sensors, no heavy loads.  If your other servos are substantial loads they can have their own ground too.  This "star" ground ensures  the charger and brain dont get confused by IR drop from common ground current.
So you are saying I need to connect the grounds of heavy loads direct to the negative of the battery?

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For switching heavy loads use FET and include a few K of gate resistance.  That way any "ground bounce" can get dissipated harmlessly.  This might cause some ugly switching but you'd rather have it there than mixed in with your low level IO.
Do you think 2k ohms will do? If I am controlling the FET's gate directly via Arduino, then sending a HIGH will switch the FET? 5v 40mA to a 2k resistor will still switch the FET?

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As the gods pointed out the Arduino battery monitor voltage will depend on loads.  Best to monitor voltage when heavy loads are idle.  You can test the battery under load, but you need to know the current and use different criteria for voltage vs charge.
I have not tried using heavy loads controlled by a uC before. If the vacuum pump + servo are running, will the voltage from battery decrease? By how much? Do you recommend other means of detecting charge of battery other than the voltage divider?


« Last Edit: January 23, 2011, 02:57:53 pm by zeitcheist » Logged

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What FET do you think will handle this?
sounds like yer already over 1 amp, the Arduino could draw 200 mA depending on how hard youre working its outputs.  And as the gods say you will probably keep upping the vvacuum motor.  For example my little home vacuum cleaner at 11 Vdc would pull about 85 amps.  So its safe to say the FET could hardly be too big.  I'm talkin 'bout a FET to switch the vacuum motor, see below you probly dont need the FET to switch the battery.

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I hope the image below will clarify what I am trying to say before. ^^
failure to communicate.  you have a charger in the dock powered by mains.  i have a charger on board the vacuum bot powered by external 15 Vdc.  two completely different approaches.  my approach requires no relay no switching, only 2 contacts between dock and bot.  The diodes and such do everything to transition between external power and battery power.

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I don't understand.
eliminate the FET and connect the battery directly to D2.

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So you are saying I need to connect the grounds of heavy loads direct to the negative of the battery?
 or else grounds of everyhting including battery to a single point.

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Do you think 2k ohms will do? If I am controlling the FET's gate directly via Arduino, then sending a HIGH will switch the FET? 5v 40mA to a 2k resistor will still switch the FET?
2k is good, even up to 10k.  sending 5v will switch on FET, the current will be nearly zero (except when the gate voltage is changing).  This is a good FET for low side switching of motors http://www.irf.com/product-info/datasheets/data/irlz44n.pdf


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If the vacuum pump + servo are running, will the voltage from battery decrease?
yes
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By how much?
no simple answer
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Do you recommend other means of detecting charge of battery other than the voltage divider?
no simple answer.  most simple answer is only measure when motors are idle.


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