Manual #3

J

Jaguarjoe

Senior Member
Maybe this is just a typo:

Manual #3 shows how to interface the uP to MOSFETs. It uses IRF530 parts. IRF530's are a poor choice to use with a uP because it is not a logic level device. The gate threshold can be as high as 4 volts and it requires 10 volts to pass full current. With a 5 volt uP output it won't be a good match up.
OTOH, IRL530's have identical specs except it only requires 5 volts to pass full current. A much better mate for a uP.
 
F

fritz42_male

Senior Member
I got caught with this - ordered some IRF530s then posted a PWM speed controller question in the forum and had it pointed out to me that IRL530s were a better choice.

Oh, well at least they are cheap and I only bought 2 of them!
 
B

BeanieBots

Moderator
Don't forget the target audience.
Driving an IRF530 will in the majority of cases work fine for on/off applications but limits the current to ~3A which avoids dangerous currents from flowing should there be a "mistake" in the circuit.
 
D

Dippy

Moderator
Yes, true, but this less-than-ideal choice of MOSFET also applies to the High Power kit (whatever the number is). I'm not really sure if the author understood MOSFETs... I'll be generous and suggest that maybe when the writing/designing was done all those years ago that logic level MOSFETs were much more expensive. And if you believe that you'll believe anything.

I'm surprised this less-than-ideal choice is still going as sensible discussions over MOSFET driving has been running on this Forum for several years.

And I'm amazed we haven't had an extra paragraph for driving devices with 3V PICAXEs..... but I'll leave that lengthy debate for another day ;)
 
J

John West

Senior Member
BeanieBots said:
Don't forget the target audience.
Driving an IRF530 will in the majority of cases work fine for on/off applications but limits the current to ~3A which avoids dangerous currents from flowing should there be a "mistake" in the circuit.
Click to expand...
If the 12 year old boy I'm tutoring in the use of the PICAXE is any indication of the target audience I'd say that what they want is a PICAXE that can control the world. He has already expressed great interest in controlling devices that draw over a KW. The lad is getting scary.

Why can't they just be happy with turning on and off an LED or some such? Why do they have to be so much like I was at their age?
 
D

Dippy

Moderator
Haha. This will start a string of reminiscing...

Yes, most of us are guilty.
One of my first projects was triac switching of the water tank immersion heater and using the cold water feed pipe as the triac heat sink.
In theory it would have worked and I had actually considered isolation. Obviously I knew more about electronics than the rest of the world (only in my mind).

Fortunately, my Dad suggested (politely but firmly) that I start my 'career' with batteries and lights and logic and 555s.
And now I have turned into my Father and suggest the same thing to others...

Been there, done it and got the T-shirt - though it doesn't fit anymore :)
 
J

John West

Senior Member
Fortunately, I've come up with a solution for the young fella's immediate control project goals - a Crydom D2475 SSR (240V AC or DC at 75A - on a substantial heatsink.) Hopefully that will meet his needs for at least awhile. After that I'm going to run and hide.
 
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Dippy

Moderator
I'm surprised the Klaxon hasn't sounded.
BAAARRP! - Mains electricity project detected - BAAARP!
Initialise Panic SubProcedure.
IF Mains or lasers or cars have been mentioned THEN GoTo Pointless Nanny Routine.
End
 
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fritz42_male

Senior Member
I remember when I was about 8 or 9 'fixing' a string of Pifco Xmas light bulbs by taking the dead ones out of sequence INCLUDING the sockets. By the time I'd taken 4 out of the string, the others were getting brighter and to test my theory, I wired one in directly to a mains plug.

The pop as the glass bulb blew itself out of the socket and over the (real) Xmas tree brought my Mum running in and resulted in a BIG row.

Lol. We were indestructible at that age - remind me never to tell you about the time I brought a bag of about a dozen Adders home thinking they were grass snakes!
 
D

Dippy

Moderator
begin lol:

OK, willco.
PLEASE, never tell us about the time you brought a bag of about a dozen Adders home thinking they were grass snakes!

end lol:
:)
 
W

westaust55

Moderator
Dippy said:
begin lol:

OK, willco.
PLEASE, never tell us about the time you brought a bag of about a dozen Adders home thinking they were grass snakes!

end lol:
:)
Click to expand...
Funnily the scenario is all too true.

I recall vividly the then young primary school teacher Back in the 70's telling of pupils delighting in bringing Death Adders to school they they had found on the way to school.:eek:
 
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Dippy

Moderator
Many years ago I donned my anorak, pulled out my metal detector and waved it around in the back field . Others had found ancient coins in nearby fields so I thought I'd give it a go.

After a while, beepbeep, and I dug up this small lump of grey grubby metal.
It felt heavy like lead.
It was a globby-droplet shape, so it was not just something that had been chopped off. About half the size of the metric thumb in size.
But it was almost pure cadmium.

Why/how it got there is still a mystery...
 
J

John West

Senior Member
The mains power work is done strictly under either my supervision or that of the lad's grandfather. We set that rule right at the start. Of course, he will break it at some point. But we do our best to make sure he knows the danger and understands it and respects it.

I was in utter ignorance when at a similar age I first cut off the end of an AC extension cord and taped the leads to a 9V battery and plugged it into mains power. If he ever does such a fool thing, he at least will not expect the battery to charge, as I did.

It's good to have just a bit of guidance when you're young and trying to understand the forces around you.

That's one reason why I'd like to see a very clear and concise manual, well thought out and detailed, with no questionable circuit implementations. This is the document that youngsters are working from when they aren't being explicitly taught by an adult. Some of them still believe everything they read. It takes a few years of them running into errors on the printed page and in their text books before they begin take everything with a suitable grain of salt.
 
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fritz42_male

Senior Member
Dippy said:
Many years ago I donned my anorak, pulled out my metal detector and waved it around in the back field . Others had found ancient coins in nearby fields so I thought I'd give it a go.

After a while, beepbeep, and I dug up this small lump of grey grubby metal.
It felt heavy like lead.
It was a globby-droplet shape, so it was not just something that had been chopped off. About half the size of the metric thumb in size.
But it was almost pure cadmium.

Why/how it got there is still a mystery...
Click to expand...
Hey Dippy, Where was this? Cadmium is bloody unusual - how did you know it was Cadmium?

I'd be kinda worried about this.

PS
Anorak? lol
 
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F

fritz42_male

Senior Member
westaust55 said:
Funnily the scenario is all too true.

I recall vividly the then young primary school teacher Back in the 70's telling of pupils delighting in bringing Death Adders to school they they had found on the way to school.:eek:
Click to expand...
Slightly different scenario - UK Adders MIGHT just kill a kid if they bite them - if the kid is small and weak.

Death Adders are a lot more aptly named!

Friend was out running in the Perth hills yesterday morning - he's an ex-pommie. He got kind of a shock when a 6ft Dugite crossed the road in front of him! He's now reconsidering rural life. lol
 
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fritz42_male

Senior Member
E

eclectic

Moderator
fritz42_male said:
OK that opens it up a little. Dorset like most of that area has had a lot of mining and probably some refining. The Cadmium might have been a trace from Zinc/Lead working & refining in the area.
Click to expand...
What a Forum!
Starting with Mosfets, we're now continuing with
Mining / Metallurgical archaeology.

Love it. :)

Tomorrow, I'll brush down ALL
of my anoraks. :))

e
 
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D

Dippy

Moderator
The metal glob was analysed used prompt (capture) gamma analysis - extremely accurate.

Near where I live was a dummy airfield in WW2.
The area was bombed enthusiastically.
Is there anything in dropped ordnance?

Other than that it is a purely agricultural area.
So, no mining in my area.
 
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