Author Topic: Smaller $50 robot using ATTINY25?  (Read 1739 times)

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Offline Razor ConceptsTopic starter

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Smaller $50 robot using ATTINY25?
« on: October 15, 2008, 06:52:52 PM »
The ATTINY25 looks like it can replace the ATMEGA8 used in the $50 robot. TINY25 can have 4 pwm channels (which drives the servos, right?), and can have 4 A/D (which is the analog to digital converter?). So this means I can make a small $50 robot using the TINY25? I'm planning on using micro servos and making a separate board for programming.

Offline Ro-Bot-X

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Re: Smaller $50 robot using ATTINY25?
« Reply #1 on: October 15, 2008, 07:05:27 PM »
Yes it will work, I have done it with Tiny26. You don't necessarily need hardware PWM for servos, but for DC motors is a must. Also, if you install jumpers or DIP switches (to disconnect the servos from the ISP pins), you don't need to remove the chip to program it.
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Offline Razor ConceptsTopic starter

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Re: Smaller $50 robot using ATTINY25?
« Reply #2 on: October 15, 2008, 07:24:12 PM »
Alright, I'm digikeying all the parts now. I'm going with a smaller 100uf capacitor. I don't think I can use an LED because the 25 has 6 pins, VCC, GND, 2 for servos, 2 for photoresistors.

About the voltage regulator, if I'm using a 4 cell nimh battery (4.8 volts nominal, a bit more fully charged), do I still run it through the 5v regulator or do I not need it as long as it still goes through the capacitor?

Offline airman00

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Re: Smaller $50 robot using ATTINY25?
« Reply #3 on: October 15, 2008, 07:35:35 PM »
the 5V regular needs at least 7V or higher to provide the 5V. If you get a low dropout regulator you would need at least 6.

Right now you can run the microcontroller unregulated at 4.8V ( yea I know this is considered bad)

Running unregulated screws up your Analog to Digital conversions , right?
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Offline Razor ConceptsTopic starter

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Re: Smaller $50 robot using ATTINY25?
« Reply #4 on: October 15, 2008, 08:59:55 PM »
About the photoresistors... the formula for the resistor is the square root of the max resisitance times the min resistance.
Say for this photoresistor here:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=PDV-P8101-ND
The max is 150kohms, and the min is 10kohms. Do the math and I would need a 38,000 ohm resistor? Are there any ones on Digikey that use a smaller resistor? The max 150kohms was the smallest maximum I could find.

Offline airman00

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Re: Smaller $50 robot using ATTINY25?
« Reply #5 on: October 15, 2008, 09:28:55 PM »
38k resistor isn't such a high value resistor . Btw why would you care if the value is high or not?
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Offline Ro-Bot-X

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Re: Smaller $50 robot using ATTINY25?
« Reply #6 on: October 16, 2008, 05:54:15 AM »
the 5V regular needs at least 7V or higher to provide the 5V. If you get a low dropout regulator you would need at least 6.

Right now you can run the microcontroller unregulated at 4.8V ( yea I know this is considered bad)

Running unregulated screws up your Analog to Digital conversions , right?

You can use a 3.3 Vreg to the analog voltage refference pin to make the A2D conversions stable. Also, make sure the Watchdog is not programmed, so the micro does not reset if servos start/stop. Try to install a big value capacitor (at 2 times the input voltage, for instance 10V) across the battery. This will account for power surges.

I have seen a tiny line follower robot that was using 2 geared pager motors (you can find them at Solarbotics) driven with a FAN8200 H-bridge (this one accepts low voltage TTL, you can find it at Jameco), a Tiny26 micro, 5 tiny IR sensors and the smallest LiPo battery the guy could find. The robot was about 3/4"x3/4" and the guy had to add some weight to it to make it change the direction properly (otherwise it would skid). He didn't use any Vreg on the robot, but he had a protection circuit for the LiPo.
Check out the uBotino robot controller!

 


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