Comperison

[adrianvon]

Hi all,
Can someone please tell me some advantages that the PIC (pic18f4455) has when compared to an 8051 ??

also, what are the advantages of using a DC motor rather than an AC motor?? does the DC consume more power since a transformer have to be used??

and what are the difference between using a DAC and a digital potentiometer when you need to vary a supply (for instance from 10mV to 1.5V??

Please need help... im confused :S

thanks in advance

 

[Sceadwian]

The 8051 is an older architecture, it's still commonly used because it's very standardized. Something like a more modern PIC or AVR based micro controller will typically have better peripherals. There is no inherent advantage from using a DC motor vs an AC motor if you don't state what you're going to be using it for, the application itself is what determines the motor type, if either type was superior all around then there would only be one type.

Understanding the difference between DAC and Digital Pot would be best answered by looking up the respective devices on Wikipedia. The voltage example you gave doesn't help, as you didn't specific resolution or current handling ability.

 

[KeepItSimpleStupid]

I'll take one of them for now.

MOTOR:
Depends on the application and the horse power. A clothes washer is now using a 3 phase motor on single these days. I used to be a two speed induction motor. Technology has changed.

A turntable that played records used to use a synchronous motor, but later went to a brushless DC design.

A toy that operates on batteries may use a Permanent Magnet DC motor.

A 500 HP electric motor will probably be 3 phase AC.

Without an application, I can't begin to say which is better.

 

[Brevor]

The 8051 is an older architecture, it's still commonly used because it's very standardized

Actually the the architecture of the PIC and the 8051 were devoloped about the same time, early 1980's. The 8051 by Intel and the PIC by General Instrument. I have worked quite a bit with 8051's and with PIC's over the years. The first time I saw the instruction set of the 18f series of PIC's my thought was that Microchip copied the instruction set of the 8051.

 

[Sceadwian]

Actually the the architecture of the PIC and the 8051 were devoloped about the same time, early 1980's. The 8051 by Intel and the PIC by General Instrument.

I was speaking of the 18F series which the original poster mentioned, which is far different from an 8051. PIC has evolved. The 8051 is a stock standard, subject to variants and spec upgrades, but 8051 compliant means something.

Personally these continual non linear upgrades in chip design and performance are why I chose Atmel's AVR line of chips when I started in electronics a few years ago, they've grown since then as well, but there's a whole lot less history and the core design is closer to being universal across the entire chip line.

I would request that any future comments on the AVR/PIC/8051 matter be left to private messages to allow this thread to help the original poster. Any further comments outside of my post #2 and Brevor's post #4 should be private to avoid muddying the waters that the poster may find something useful here without being saturated with too much information and too many viewpoints.

 

[adrianvon]

Thanks for your fast replies guys...
the motor will be used to roll a canvas cover (75" by 74"). This cover will be on the roof so it will be exposed to elements such as high winds, therefore the motor has to be a little bit strong. The problem is that i want to keep my project as low in power consumption as possible. I think an AC motor will consume less power since no transformer and supply will be needed, but will it be possible to control an AC motor with low speed? are they more expensive then the DC motors?

Regarding the DAC and digital pot, the current will be approx 50mA not more and the higher the resolution the better... but what i want to know is a comparison between general DAC and digital pots.

thanks again for your help

 

[Sceadwian]

What is the expected actuation rate of the cover? (number of cycles per minute/hour/day/week/month)

 

[KeepItSimpleStupid]

OK, what do you plan to do with a DAC/Digital Pot in your application?

 

[adrianvon]

I want the cover/shutter to fully close/open in about 10 to 15 seconds. The DAC or digital pot will be used since the cover will close when a pre-set temperature is reached. A voltage comperator will compare the voltage of a temperature sensor with the pre-set temperate. To set the reference temperature a 4*4 key pad will be used, therefore i need to use a DAC or a digital pot to convert the inputted temperature to analog (for instance if i want the shutter to close at 24oC, i press 24 on the key pad and the DAC or digital pot converts it to 240mV which is equivalent to 24oC) . The bigger the resolution the better since it will more 'steps' and be more accurate.

 

[adrianvon]

Any help please...

 

[adrianvon]

the reason that i want to know the advantages of using PIC over 8051 is that during the interview, the lecturers will ask my why i have chosen this MC instead of others, but i dont have a particular reason for choosing a PIC MC.

By the way, can a servo motor be used for this application?? or are servo motors only used for small applications??

 

[Robin2]

There is a big difference between power (watts) and energy (watt hours). It seems to me you need a suitably powerful motor (to make the cover close quickly) but you may not need much energy if the opening / closing is not very frequent. If the motor is powered (say) from a 12v lead-acid battery you would have plenty of watts to activate the motor and the battery could be recharged slowly and continuously using a low wattage charger.

A low voltage DC motor will probably be much easier and safer to control than a mains voltage AC motor. However be conscious of the fire risk from high short-circuit currents from batteries.

As far as I know any motor can be a servo motor - it just depends on the power requirement. But perhaps you have a specific part in mind when you use the term "servo motor"?

 

[adrianvon]

Thanks for your reply Robin2,
I will not use a battery to operate the motor. If i used a DC motor i have to build a power supply for it.
will a stepper motor shaft be stiff when there is no supply? (like a servo)... because if not, the wind that hits the shutter/cover can cause the motor to rotate (which i don't want)
And is a stepper motor ideal for this type of application?

thanks

 

[KeepItSimpleStupid]

Darn, lost a post:

You may wish to consider a low voltage gear reduction AC or DC motor.

With Gear reduction, there is less chance that the roll will move. With worm drive, it can't.

Low voltage: Safety

DC might be better than AC because with DC it isn't easy to add over torque protection.

I did a drapery controller once before they really existed on the market. I used a 24 VAC synchonous motor with limit switches and a clutch. In a worst case scenereo, the chain would jump the gear. Everything was exposed. Some 30 years ago. Torque was about 20 oz-in

You need to know that.

 

[KeepItSimpleStupid]

I think your temperature measuring might have flaws. It's always tricky.

Why a Keypad for temperature input?

 

[carbonzit]

How else would the user set the temperature?

 

[carbonzit]

Just installed remote-controlled window shades (from Sunsetter) on a friend's house recently. One of them failed, so I had to go up the other day and take it down. We looked inside and saw the motor: surprisingly small, including all the electronics. About the size of a small clock-drive motor, or a small "pancake"-style stepper. Geared, of course. So you don't need a very big motor if it's geared down.

 

[KeepItSimpleStupid]

carbonzit:

1. Keypad
2. Rotary Encoder
3. UP/DN Buttons
4. Touch Screen UI
5. Thumbweel switches
6. Web enabled
7. Smartphone App
8. IR remote control
9. RF remote control

For starters.

 

[Robin2]

Thanks for your reply Robin2,
I will not use a battery to operate the motor. If i used a DC motor i have to build a power supply for it.
will a stepper motor shaft be stiff when there is no supply? (like a servo)... because if not, the wind that hits the shutter/cover can cause the motor to rotate (which i don't want)
And is a stepper motor ideal for this type of application?

thanks

I think you are getting mechanical and electrical issues mixed up.

If you need a force to prevent the shutter from moving don't use the motor for that - use a mechanical system. The simplest mechanical system is probably a worm gear which also provides a large torque increase (speed reduction) so a smaller motor would work. Alternatively you could have a mechanical pin lock (solenoid operated?) or an over-centre lever mechanism.

You will need a DC supply for your control system and that will need to be derived from mains power so why not use a 12v DC motor system. The 12v battery could be charged from the mains by a cheap 12v trickle charger and none of the stuff you make would have to work at mains voltage.

Normal electric motors rotate freely when they are disconnected from the power. I suspect that any that don't have expensive mechanisms inside to act as a brake.

ETA You could use a potentiometer to allow the user to set the temperature (which sets the threshold voltage directly). When you have it working just add a suitably calibrated dial from a piece of card or plastic.

 

[adrianvon]

Thanks for your replies guys
I think a DC motor with a worm gear (as Robin2 said) will work fine for this application...

Why a Keypad for temperature input?

The original design was with an UP and Down buttons, but the lecturer told me to use a key pad instead to set the reference temperature.