Show Posts
Pages: 1 ... 70 71 [72] 73 74 ... 86
1066  Forum 2005-2010 (read only) / Interfacing / Re: Provide more current to servos when they need it? on: June 25, 2010, 02:17:46 am
I've got 4 AAA batteries in a battery pack supplying 6v to a LM317 voltage regulator which is configured with two resistors to output 4.8v.  

This is connected to the positive and negative rails on my breadboard.

The power lines for the two servos are attached to these rails.

After the servos, I have a 47uF capacitor and a 0.1uf capacitor bridging the two rails.  The electrolytic is connected so the negative pole is on the negative rail and the positive pole is on the positive rail.

After that on the rails is everything else.  The AMmega, a multiplexer connected to a dip switch, and a shift register for controlling the leds.

It's fairly straightforward.  I guess I can post a photo of the breadboard tomorrow.  I don't know what you expect to find though.
1067  Forum 2005-2010 (read only) / Interfacing / Re: Provide more current to servos when they need it? on: June 25, 2010, 12:24:32 am
I picked up a 4 AAA battery pack at Radio Shack, so I'm now running off 6v as stated originally with a 4.8v regulator.

I also grabbed an IN4001 diode:
http://www.radioshack.com/product/index.jsp?productId=2036268

I meant to grab the IN4004 diode:
http://www.radioshack.com/product/index.jsp?productId=2036270

Which GrumpyMike has in his motor tutorial, but apparently they had the bags mixed up.  I think they're interchangable.  I can't tell the difference between them, besides the 4004 being good to 400v and this one being good only to 50v.  I don't know if that matters.

And I grabbed a 100uF capacitor.  The 470uF capacitors they had were way too big for this project.  I'm hoping 100uF is suitable.

Unfortunately, they didn't have any small inductors, so I couldn't get one of those.  Can't be sticking a coil of wire an inch and a half long on this board.


Anyway, the project runs as well off the 4 AAAs as it did off the 6 AAAs.  Which is to say, it runs, but the LEDs still dim when I activate the servos.

I'd still like more information about these changes being suggested.  For example, how is adding a diode going to solve the issue of the batteries not being able to supply enough current?
1068  Forum 2005-2010 (read only) / Interfacing / Re: Provide more current to servos when they need it? on: June 24, 2010, 07:11:04 pm
Quote
Power the rest of the circuit thru a low voltage drop (.1v) diode

I'm loooking on Mouser, and I can't find any diode near that.  .3v was the lowest I could find.  Most were at least .5v.
1069  Forum 2005-2010 (read only) / Interfacing / Re: Provide more current to servos when they need it? on: June 24, 2010, 06:32:09 pm
Quote
It's a little surprising to hear that AA batteries are underpowered for servos

I'm using AAAs here.  But I know someone has built this same circuit powering two servos and he used a 9v battery.  What I don't know is how he got away with that because my leds dim quite a bit when I try to use a 9v.
1070  Forum 2005-2010 (read only) / Interfacing / Re: Provide more current to servos when they need it? on: June 24, 2010, 06:09:42 pm
Quote
Power the rest of the circuit thru a low voltage drop (.1v) diode, and use a high value capacitor down stream of the diode to minimize the voltage disturbance to the circuit.

So place the diode where, on the positive rail, or ground?  

And what exactly constitutes a high value capacitor here?  I know capacitors can be huge or tiny, and I have no idea what size would be appropriate in this instance.

The cap goes across the positive rail and ground I assume.
1071  Forum 2005-2010 (read only) / Interfacing / Re: Provide more current to servos when they need it? on: June 24, 2010, 06:00:53 pm
Quote
You REALLY REALLY want to ISOLATE the Servo Supply from the rest of the circuit.  Your current solution will still let the servo loading and spiking to impact the stability of the pseudo 5V source you now have relying on voltage drop on diodes.

Diodes?  What diodes?

Are you talking about that schematic up there?  That's not my circuit.


Quote
You REALLY REALLY want to ISOLATE the Servo Supply from the rest of the circuit.

Okay, but WHY do I want to do this?  Because of these dips in current?  Because they introduce noise to the voltage supply?   Because they might blow stuff up?

In my circuit (not the one pictured above) I've got a 47uf and a 0.1uf capacitor after the servos to try to remove noise.  

Do I need more than that?  I know GrumpyMike suggests inductors after motors, but I've heard protection diodes and those sorts of things aren't really necessary with servos.  And I haven't seen any schematics with servos that have inductors.  If I do need an idncutor here, I'll have to go get one.  But I don't know what size I need.


Quote
If it were me, I'd be dedicating a separate 7805 to the logic board and installing extra capacitors for assistance with spikes and dips.

I don't understand how that will help.  Remember you're talking a newb here.

How will a voltage regulator solve my current supply problem?  If the servos are sucking up all the current, isn't the voltage still 4.8v?  How is a voltage regualtor gonna fix that?
1072  Forum 2005-2010 (read only) / Interfacing / Re: Provide more current to servos when they need it? on: June 24, 2010, 05:50:45 pm
West,

Sorry, you're right, the supply is currently 9v.  The plan is to move it to a 4 AAA supply when I get such a battery pack.
1073  Forum 2005-2010 (read only) / Interfacing / Re: Provide more current to servos when they need it? on: June 24, 2010, 03:58:09 pm
They're sub-micro servos, and there are two of them.  They're powered with 4.8v supplied by a regulator connected to 6 AAA batteries providing 6v.  The regulator also supplies power to the rest of the circuit, which draws maybe 50-100mA.
1074  Forum 2005-2010 (read only) / Interfacing / Provide more current to servos when they need it? on: June 24, 2010, 03:20:05 pm
So besides switching from AAAs to AAs, is there any other way to smooth out the spikes in current draw when my servos activate?

I tried a 47uf capacitor, but that didn't do anything except stop my AtMega from freezing up occasionally, after activating them, presumably due to noise in the lines.  (I placed the 47uf capacitor after the servos on the +5v and Gnd lines going to the rest of the circuit, and did the same with a 0.1uf capacitor.)

Would a larger capacitor do the job?  The servos I'm guessing drawing around 200mA each when they activate, possibly up to 400mA when they reverse.

Or is an inductor needed here?

Or will neither of these provide the little extra bit of juice I need to avoid having my LEDs dim slightly when the servos activate?
1075  Forum 2005-2010 (read only) / Interfacing / Re: Ribbon cable connection? on: June 17, 2010, 06:58:12 am
I wonder if anyone's ever tried to make a minature CNC machine with one of those?
1076  Forum 2005-2010 (read only) / Interfacing / How is my Arduino Pro Mini running off 4.5v? on: June 23, 2010, 08:24:16 am
I have a 5v Pro mini.  I connected my 4.5v supply to VCC and GND to try powering it.  I expected that this would work as it is within specs.  It did.

Then just for kicks, I connected the 4.5v supply to the RAW pin and GND.  I expected that this wouldn't work because despite the onboard regulator being a low dropout regulator, it still needs something like 5.35v, and perhaps more if it has that diode in front of it Grumpy Mike's power regulation tutorial mentions which would drop the input voltage by 0.7v.

So how is it the Arduino is working?  I thought below the dropout voltage the regulator stops working?  Or does the dropout voltage simply mean that below 5.35v it can't supply 5v, but it will continue to supply something less than that, and cease functioning as a stable source of power?

If it's the latter, well, I guess that's great actually.  I mean the Arduino can run at less than 5v, so this potentially means more battery life for my device...

But still, I wonder what happens to the voltage from the regulator when you get into this condition?  If I'm supplying 4.5v, do I get 4.5v out, or something less than that, like 4.5v = minus the dropout voltage, minus whatever the diode takes away?
1077  Forum 2005-2010 (read only) / Interfacing / Re: Chip Select on: June 23, 2010, 08:28:06 am
Okay...  I would not be sharing the common pin in this circuit, so I guess I don't need to disable it, but that's good to know.  I suppose I might eventually want to run multiple multiplexers and connect that same input pin to more than one.
1078  Forum 2005-2010 (read only) / Interfacing / Re: Chip Select on: June 23, 2010, 07:09:48 am
When you say outputs, you mean the eight input/outputs I can select between, right?

The multiplexer is being used to read a dip switch.  So the switches are connected to ground and to the multiplexer's input/output pins, and the common pin goes to an input pin on the Arduino which has its internal pull up turned on.

The three select lines which choose which input/outputgoes to common are the ones which would be shared between the other two chips.

If disabling the chip causes the inputs/outputs to float... then what would that mean?  That the common pin would gloat as well?  Since I won't be reading it, that wouldn't matter.  And besides, it would be pulled up.

Or are you imaginging that I have something connected to the input/outputs which might blink or corrupt something else if the pins are allowed to float?  I don't see an issue there as well since they're just connected to switches.

Also, now that I think about it, I wonder if I would need to use the 4051's select line at all?  Let's say I don't disable the input/outputs?  What will happen if I, say access the shift register?  The 4051 will jump rapidly between different input/outputs, right?  But since I know that I'm not reading them at that time precisely because I'm accssing the shift register, it doesn't matter.  It's not like I'm reading the common pin on it, or that toggling the outputs is going to create any visible display, since all it is hooked up to is dip switches.

My only concern here is if this would have some effect on the shift register, but I don't have any idea if that might be the case.
1079  Forum 2005-2010 (read only) / Interfacing / Chip Select on: June 22, 2010, 01:09:09 pm
Hey guys,

In my latest project, I'm using the following chips:

CD74HCT4051 multiplexer:
http://focus.ti.com/lit/ds/symlink/cd74hct4051.pdf

TPIC6B595 power shift register:
http://focus.ti.com/lit/ds/symlink/tpic6b595.pdf

But I'm also interested in adding sound to my project, so I was thinking about using this dac:

MCP4921 DAC:
http://ww1.microchip.com/downloads/en/DeviceDoc/21897a.pdf

Here's my question.

These three chips seem to use completely different methods of communicating with the Arduino.  Yet all three seem to need only three pins to communicate with them, and all three seem to have a forth pin which can be used to enable or disable the chip.

The multiplexer has E which is active low.  Pulling it low enables the inputs/outputs.

The shift register has G which is also active low.  I believe this equates to OE or Output Enable in the http://www.arduino.cc/en/Tutorial/ShiftOut example.  The data sheet indicates that pulling G low enables the chip, while pulling it high erases the input buffer and disables the outputs.

Lastly, the DAC has CS or Chip Select, which is again active low.  Pulling it down enables the serial clock and data functions.


Regarding the inputs...

On the multiplexer, the three inputs are basicaly used as a binary number to select the output which is active.  There is a fourth line which is needed to read the output, but for the purpouses of this discussion, I don't think that's important.

On the shift register, you've got the data pin, the clock pin, and the latch pin.

And on the DAC, you've got the same thing, a data pin, a clock pin, and a latch pin.  Okay my bad, there aren't three different setups here, I saw SPI mentioned in the DAC docs but apparently the clock is merely "SPI compatible", and there's no return data line as in an SPI setup.


With that out of the way, my question is this:

Could I theoretically hook all three of these chips up to the Arduino with just seven pins?  

Three to select which chip I want to enable, another three which would be used either to select the multiplexer input, or to send data to the shift register or dac, and one more to read data from the multiplexer?

I know the dac would require some high speed data output, but the multiplexer would only need to be read once on bootup as that's used to read some dip switches.  And the the shift register is used to run a few leds and won't need to be updated more than 30-60 times a second.

And even if the dac does need its own dedicated lines, could I still do this with the multiplexer and the shift register?  If I have both chips seperate, then I'd be using 7 pins, but I could save a pin if I tied their data lines together and used the chip select stuff.  Not much, but a pin is a pin.  

What do you think?
1080  Forum 2005-2010 (read only) / Interfacing / Re: Touch switch on: June 22, 2010, 04:45:47 pm
In regards to the touch switches, I can report that the 1M resistors I'm now using are working great!  There is next to no noise.  I might get values up to 2 on the switch that isn't being touched and the one which is being touched no matter how lightly reads at least 20, but more often in the range of 100-200, and 300 if I press hard.  

The above is with a dry finger.  With a wet finger it jumps to 900, though you can see it drop as the finger dries off.
Pages: 1 ... 70 71 [72] 73 74 ... 86