More dumb questions

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2camjohn

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Hi

I have some quick questions regarding PICs, Specifically the 18f84a and the 16f628.


Will these chips work fine on 6V ?

How much current can these chips provide per pin? (only one output requires much current, i have 2 more ouputs just controling LEDs)

Can someone point me in the direction of a good tutorial based website on current amplifiers. I would like something small in size using common components.


Many thanks
 
2camjohn said:
Hi

I have some quick questions regarding PICs, Specifically the 18f84a and the 16f628.


Will these chips work fine on 6V ?
Click to expand...

They seem quite happy at 6V, I've used then a lot off 6V batteries.

How much current can these chips provide per pin? (only one output requires much current, i have 2 more ouputs just controling LEDs)
Click to expand...

It's in the datasheet, it's something like 30mA, what are you wanting to control.

Can someone point me in the direction of a good tutorial based website on current amplifiers. I would like something small in size using common components.
Click to expand...

Assuming this is to drive something from the PIC, you're not asking the right question!. Tell us what you are wanting to do and we can probably help, but I'm presuming you don't really want a 'current amplifier', just something to provide a higher switching current than a port pin on it's own.
 
2camjohn said:
Im driving a 6V low pressure (100psi) solenoid.
Click to expand...

It's nice to know it's 100psi, but that doesn't give any details about it's current requirements - do you know what they are?.
 
Im sorry I dont know the current requirements.

I cant measure the current as the pulse is so tiny (14ms) so my multimeter doesnt pick it up. I dont have an oscilloscoope either



I just want something that switches quickly and accurately, about 1A at most.

It needs to be small too.

Thanks
 
I cant measure the current as the pulse is so tiny (14ms) so my multimeter doesnt pick it up. I dont have an oscilloscoope either
Click to expand...

With the multimeter measure the resistance of the 6V solenoid and apply ohm's law.
 
2camjohn said:
Im sorry I dont know the current requirements.

I cant measure the current as the pulse is so tiny (14ms) so my multimeter doesnt pick it up. I dont have an oscilloscoope either
Click to expand...

It doesn't matter about the existing pulse width, simply disconnect it and feed it from a 6V battery with your ammeter in series - and measure the current - easy!.

As the pulse width is so small, and presumably the repetition rate isn't high?, you can probably use a fairly small transistor. But you do need to know the current required!.
 
OK I tested my solenoid.

It comes out at 70 ohms which works out at 80mA at 6V.

So can someone recommend a circuit which will easily drive an 80mA solenoid.

I want it to be very accurate and fast at switching (+- 2% of the 14ms pulse) and it needs to be as small as possible.

Many thanks
 

Just use a small NPN transistor (I'd use a BC107 - but I always do!), connect the emitter to ground (0V), and the base via a 1K resistor to the I/O pin of the PIC. The solenoid goes from the collector of the transistor to the +ve rail - be sure to fit a reverse biased diode across the solenoid (cathode to +ve, anode to collector). There should be no problem about speed, the slowest thing (by a huge margin) will be the solenoid.
 
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