Author Topic: Minimum OOPic Voltage  (Read 2052 times)

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Offline vivek9856Topic starter

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Minimum OOPic Voltage
« on: March 13, 2008, 05:03:22 PM »
I need to power the following:

1 - OOPic R
1 - Serial LCD
2 - 5 V, 0.5A Stepper Motors driven through an L298N

with four 1.5 V cells. I need to figure out how to do this.

With the PIC plugged into a 12V bench supply, and the two drivers plugged into a 5V bench supply, everything works just fine. When the OOPic and LCD only are plugged into four alkaline D cells, the OOPic barely boots the LCD and just barely runs. When the Pic, LCD, and stepper are plugged into the four D cells, the EAC light on the PIC starts flashing rapidly, the motors jerk a bit, and the LCD barely is on. Nothing is working.

So I need your help on choosing the right batteries and doing whatever else I need. I thought about doing the following:

1) Bypassing the onboard PIC logic regulator and replacing it with an L2594 LDO 5V regulator (Put a fairly large cap (400 uF??) between input and ground, and a small 5 uF between output and ground)
2) Switching from regular Walmart Alkaline D cells to either (Four AA 1.2 V NiMH (2300 mAh each) batteries) or (four D 1.5 V Industrial Alkaline Energizer EN95 batteries (Supposedly rated for 20,500 mAh!!!))

Would this work? I would appreciate it if you could give me an answer quickly, especially regarding a battery choice (Or another one if you have an idea) and what size caps I should use on the voltage regulator / battery to cover for dropouts when the motors rev up.

Lastly, the bipolar stepper motors I have barely have any torque (They are supposedly rated to 211 oz/in, which I thought was a lot). Is there any way to increase my torque (besides lowering speed) through the OOPic? Right now, I am using the oStepper object to run the steppers under phasing 0.

Thanks in advance!

Offline 555 timer chip guy

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Re: Minimum OOPic Voltage
« Reply #1 on: March 15, 2008, 02:42:50 PM »
Ya you do need more power, make sher that you use a battery with a higher specifications that what you actual need for example if you need 5v 3 amps you should use a 7 to 12 volt and at least a 4 amp battery. That is because when you were drawing power from that 6 v pack it drops to about 4 volts or less depending on the current so always have more battery power than you need.

Offline vivek9856Topic starter

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Re: Minimum OOPic Voltage
« Reply #2 on: March 15, 2008, 06:31:55 PM »
I can not use higher voltage batteries as I am limited to 6V. However, I was thinking about building a DC voltage boost circuit (I believe its called a Buck-Boost circuit?)

Would this be a viable option for me, or would it not work at all?

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Re: Minimum OOPic Voltage
« Reply #3 on: March 16, 2008, 07:42:37 PM »
Just swap out that voltage regulator for an LDO with like a .3V or .5V drop and you will be fine.

Offline vivek9856Topic starter

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Re: Minimum OOPic Voltage
« Reply #4 on: March 16, 2008, 08:51:05 PM »
Just swap out that voltage regulator for an LDO with like a .3V or .5V drop and you will be fine.


Thats what I was originally doing. Secondly, I just applied a reverse voltage to my OOPic, so I fried the logic voltage regulator. So, I'll have to replace it anyways.

Heres my plan.

- Swap out the logic regulator for a LM2940
- *****Use the EN95 batteries
- Put diodes on the OOPic input (To prevent reverse voltage


** - For the EN95 batteries - Are they worth it? According to what I think, the higher the mAh rating of a battery, the following occurs:
     When heavy current is pulled, their voltage drop is less than regular batteries
     They can provide more current than regular batteries
     They last longer than regular batteries
Right?

Also, for the OOPic power diodes, if I put one allowing current to go through to the positive, and one to come out of the negative, if I ever apply power the wrong way, the diodes will protect the OOPic?

Thanks!

Offline Ro-Bot-X

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Re: Minimum OOPic Voltage
« Reply #5 on: March 17, 2008, 12:48:04 AM »
Yes, the diodes will protect the OOPic, but they will have a voltage drop of 0.6V to 0.8V per diode. I would just replace the connector to the battery for a polarised one and forget about the diodes. If battery capacity is not limited, use one with high amperage rating, since it will last longer and have less voltage drop when the motors switch directions. And increase the value of the input capacitor to about 1000uF / 25V or 50V.
Check out the uBotino robot controller!

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Re: Minimum OOPic Voltage
« Reply #6 on: March 17, 2008, 04:45:46 AM »
More specifically, get an LDO with reverse voltage protection built in. ;D

(its saved me one two occasions already)

Offline vivek9856Topic starter

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Re: Minimum OOPic Voltage
« Reply #7 on: March 18, 2008, 03:27:17 PM »
More specifically, get an LDO with reverse voltage protection built in. ;D

(its saved me one two occasions already)

I bought a LDO regulator with RVP built in, however, I thought that this meant that when reverse voltage is applied, the regulator will blow and protect the circuit from a reverse voltage. Does RVP mean that after applying a reverse voltage that the regulator will continue to work?

Also, about the battery capacitor, it would be beneficial to put a 1000 uF capacitor across the poles of the battery, between + and ground right (In parallel w/ the battery output)? Would this affect the battery drain rate, current providing ability, or voltage? Or will it just keep the battery output the same when a high current load is turned on momentarily such as motors?

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Re: Minimum OOPic Voltage
« Reply #8 on: March 21, 2008, 09:19:27 PM »
Quote
I bought a LDO regulator with RVP built in, however, I thought that this meant that when reverse voltage is applied, the regulator will blow and protect the circuit from a reverse voltage. Does RVP mean that after applying a reverse voltage that the regulator will continue to work?
Ehhhh mine have never blown . . . I'm not sure how long the voltage can be reversed or how high of a voltage, or if all reg's are the same, but it shouldn't blow if its a good reg.

 


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