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SparWeb

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Joined: 17/04/2008
Location: Canada
Posts: 196

Posted: 10:08pm 16 Apr 2008

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Hi,
Gotta start by saying thanks for the PicLog - it's just what I've been looking for. I have most of the components I need: I've been playing with a PicAXE 18X for a while in this direction, but I found the standard board can't be mounted on anything.

Two questions come to mind: why do you need the 1N4004 diodes on the opto-isolator? Three in series offers a total 1200V reverse voltage - wouldn't a series of 1N4001 be enough? (I'm asking because I have lots of those).

My second question is why is there a 180 ohm resistor on the picaxe serial wire?

Steven T. Fahey

Gizmo

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Joined: 05/06/2004
Location: Australia
Posts: 5116

Posted: 10:32pm 16 Apr 2008

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Hi Steven, welcome to the site.

The three diodes in series form a crude voltage limiter to keep the voltage to the optocoupler input at about 1.8 volts ( each diode has a voltage drop of about 0.6 volts, so 3 in series give us 1.8 volts ). Yes the 1N4004's could be replaced with 1N4001's.

The 180ohm resistor is just the recommended value as show in the PicAxe manual. It can be left out but for noisey evironments or long serial cable lengths they recommend you leave it in.

Glad you like the PicLog. Some of the forum members are working on improving its currrent measurement circuit, its a bit limited as is.

Glenn

The best time to plant a tree was twenty years ago, the second best time is right now.
JAQ

SparWeb

Senior Member

Joined: 17/04/2008
Location: Canada
Posts: 196

Posted: 03:37am 17 Apr 2008

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Thank you. Time to heat up the solder iron!

I've seen some of the current measurement discussion so far. I'm not too keen on using a shunt, either. I've seen some homemade current transformers that I might try. That will take some experimentation, too, of course.

PS I like the look and organization of the site. As you may recognize from my handle, I'm a long time member of the "other" forum. I only recently "rediscovered" the Backshed, having originally found it and read a lot of the material over 4 years ago. Lots changed since then!

Thanks Glenn

Steven T. Fahey

GWatPE

Senior Member

Joined: 01/09/2006
Location: Australia
Posts: 2127

Posted: 04:14am 17 Apr 2008

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Hi Steven,

I have become a fan of the Alegro hall effect devices. You should use a carrier board, but they have very low insertion losses, linearity, galvanic isolation and work well with a micro. There may be other brands that do a similar job. The output for 0 amps is half rail, but this should not be a problem.... Gordon.

become more energy aware

SparWeb

Senior Member

Joined: 17/04/2008
Location: Canada
Posts: 196

Posted: 02:21pm 18 Apr 2008

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Thanks for the help so far. I decided to make mine "modular", so I spent an hour last night assembling the RPM board - AC in, through the optocoupler, and pulses out. Seemed like a good start since I don't have a lot of soldering practice. I will end up with 3 separate small boards, and I will have the flexibility to replace one if it doesn't work, or an improvement is possible.

Steven T. Fahey

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