The MagPi Magazine - Aimed at learners - Printed edition Kickstarter

Hi All,

Thanks for the helpful comments.  I think the main problem is that the transistor was selected incorrectly and that probably shifted the expectations of what it would be able to achieve.  I fear that the circuit probably won't be workable in it’s current state, as a transistor able to switch the power required and still only need a low base current is going to be hard to find (without using Darlington pairs or something else - negating the hope to make it a simple circuit). The circuit did apparently work, but I can't confirm myself how well or how long it was tested for.

I'm not sure what the best option is regarding the article at the moment.  But the team is looking at the options and hopefully we can get it resolved.

A simple design which is close as possible to the principle involved would be helpful, would replacing the transistors with suitable Darlington Pairs be enough (with the calculations re-done) - I've not looked yet to see how the numbers stack up (I don't do electronics enough to have all the numbers/calculations in my head like some of you probably do).  Anyway, a fix for the current design and some words to suggest that better engineering solutions will be discussed later may be the best option (if nothing else, dropping the control pins down to 2 is worth a new circuit, and obviously suitable driver ICs can be talked about).

I've been looking at other designs (was looking at making a basic h-bridge anyway for my own projects), but yet to try any out and they wouldn't really fit into what the article was attempting at that point.

I hadn't noticed that the topic had been locked on the RPi forum, but I imagine they try to keep a tight ship there to avoid things descending into fights, or upsetting people (particularly since they have a lot who aren't used to forums).  To be fair, most people should be able to have any discussion when faced with such limits with some effort.

As for the comments about a spending money on a good text book, I totally agree there, since there is no way the information in the magazine would be as detailed or as structured as a book.  However, we hope that the magazine will inspire people to get to the stage where a textbook on the subject would be interesting and useful to them.

Also fair comment about lower level options on the kickstarter...this wasn't done on purpose, just not something we thought of at the time and we wanted to avoid making the printing complicated by splitting things.

Thanks again for being kind.

meltwater.

Hi All,

Thanks for the helpful comments.  I think the main problem is that the transistor was selected incorrectly and that probably shifted the expectations of what it would be able to achieve.  I fear that the circuit probably won't be workable in it’s current state, as a transistor able to switch the power required and still only need a low base current is going to be hard to find (without using Darlington pairs or something else - negating the hope to make it a simple circuit). The circuit did apparently work, but I can't confirm myself how well or how long it was tested for.

I'm not sure what the best option is regarding the article at the moment.  But the team is looking at the options and hopefully we can get it resolved.

A simple design which is close as possible to the principle involved would be helpful, would replacing the transistors with suitable Darlington Pairs be enough (with the calculations re-done) - I've not looked yet to see how the numbers stack up (I don't do electronics enough to have all the numbers/calculations in my head like some of you probably do).  Anyway, a fix for the current design and some words to suggest that better engineering solutions will be discussed later may be the best option (if nothing else, dropping the control pins down to 2 is worth a new circuit, and obviously suitable driver ICs can be talked about).

I've been looking at other designs (was looking at making a basic h-bridge anyway for my own projects), but yet to try any out and they wouldn't really fit into what the article was attempting at that point.

I hadn't noticed that the topic had been locked on the RPi forum, but I imagine they try to keep a tight ship there to avoid things descending into fights, or upsetting people (particularly since they have a lot who aren't used to forums).  To be fair, most people should be able to have any discussion when faced with such limits with some effort.

As for the comments about a spending money on a good text book, I totally agree there, since there is no way the information in the magazine would be as detailed or as structured as a book.  However, we hope that the magazine will inspire people to get to the stage where a textbook on the subject would be interesting and useful to them.

Also fair comment about lower level options on the kickstarter...this wasn't done on purpose, just not something we thought of at the time and we wanted to avoid making the printing complicated by splitting things.

Thanks again for being kind.

meltwater.

@Graham

Yep that circuit looks similar to the one I had in mind (was writing my post as yours was posted it seems).  Also, I'd not tried it yet or I probably would have suggested it at the time.

The answer to why have the other one in Issue 8, it was the author's aim to try to show how they got to their solution they had used.  Obviously this is a problem with having a small amount of resource and time available to cover everything we need to.  I think the whole thing does show that often such things aren't going to be clear to beginners either, which was what was trying to be addressed (even if incorrectly).

The series of articles which this one is from is a great project and I think that it is great they have taken a lot of time to try to explain what they are doing and how they are doing it.  Even if it is just in their spare time.  Highly commendable I think.