catmaker
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Re: Please design a Primary School Board

Sun Aug 19, 2012 5:03 pm

I know your target is primary school D&T, but just on motors:
1. How big/little (V/A) a motor are you talking about?
2. DC brush/3-phase brushless/stepper-unipolar/stepper-bipolar?
3. Sensor-less/sensored/(censored)
4. Geared/non-geared/torque required?
5. Attached to what?

Different motors require different drive-electronics.
Show us pictures/diagrams of your intended motor-gadget.
MAybe you could help collate a set of pictures.

simplesi
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Re: Please design a Primary School Board

Sun Aug 19, 2012 6:18 pm

Lets define it as 12V at 1A like one of these
http://www.knexusergroup.org.uk/acatalo ... =uk#a92815
Which probably is a DC brushed, sensor-less, geared one.
Attached to what?
Fairground ride made out of knex,wood,cardboard or a robot wheel drive etc :)

This sort of chip might do the job (if it was full H bridge as we need it reversable :) ) https://www.sparkfun.com/products/315 but maybe better/cheaper to build a discrete circuit

Simon
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tech_monkey
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Re: Please design a Primary School Board

Sun Aug 19, 2012 7:22 pm

Finally its only taken 27 posts to get to this point. Wouldn't it have been better to have said all this at the beginning.
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simplesi
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Re: Please design a Primary School Board

Sun Aug 19, 2012 7:29 pm

Wouldn't it have been better to have said all this at the beginning.
Well time don't go backward so lets all start again and treat it as the 1st technical question/answer :)

Simon
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techpaul
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Re: Please design a Primary School Board

Sun Aug 19, 2012 9:11 pm

Lots of boards already exist and I have some that need assembling and testing, that do part of what you want and allow the addition of other components..

See Board with 3V to 5V translation of all signals, ESD protection and a 16 bit GPIO I2C port with prtotype area for other parts on a board size less than 4in x 3in ( 99 x 74 mm).
http://www.pcserviceselectronics.co.uk/ ... Layout.pdf
Basic Breakout as above no 16bit GPIO chip
http://www.pcserviceselectronics.co.uk/ ... 20View.gif
and close up of prototype Area 0.1in spacing vias and some tracks
http://www.pcserviceselectronics.co.uk/ ... 20Area.gif

These have been done in Eagle, and take time to build.

I have the PCBs and parts in my hands now, including a simple 7 seg display and switch, as a much smaller PCB and 1inch 7 seg display.

No cables to Pi, just plug onto the Pi GPIO. Working on wiring and python tutorials, for many things including serial SPI and I2C.

Be aware that there are certain safety regulations or education authority rules, that dictate you cannot have more than 20V DC as an open voltage, cannot put my finger on the current at moment, other speeds and forces of objects.

Please also bear in mind the newer devices are ONLY coming out in SMD so you have to make a PCB or add a Schmart board to breadboard/stripboard to anything useful these days.

A lot of DIP parts are still available but they are mainly OLD parts and are larger.

Look at your Pi and see if you can find more than 6 DIP parts that are NOT connectors.
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simplesi
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Re: Please design a Primary School Board

Sun Aug 19, 2012 9:48 pm

Great stuff but I'm not after a generic/exapndable design - I'm just after the one :)

Simon
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techpaul
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Re: Please design a Primary School Board

Sun Aug 19, 2012 10:03 pm

You are missing the point, boards like these give you a chance to dabble and add bits to see what works and what does not work. Then you might be able to dteremine a FINAL specification that soemone can design and TEST a circuit for.

At the moment you have vague hand waving, and a SHORT time scale and expect a circuit to just appear.
I could in 30 minutes give you a circuit, but I could guarantee with 100% certainty at least some part of it will
either not work at all, work some of the time or not work as you intended, but not communicated.

You will waste two to three weeks of building and trying and exchanges over why it does not work and most likely give up in frustration.

Most people will only be interested in getting a general design done for many places not doing just your one. This is because they understand the amount of time, sweat and toil involved.

What you are asking for in real life gets charged out to companies at around 500 to 1500 pounds per day of consulting/design time and parts and other materials. People will only be interested in the effort for making something that is going to be easily repeated.

I and others have lots of experience of those who come along with vague hand wavings and 99% of the time they end up as dead end projects.
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simplesi
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Re: Please design a Primary School Board

Sun Aug 19, 2012 10:39 pm

I could in 30 minutes give you a circuit
Thats the sort of thing I'm after :)

If nothing else, we'll get a ball-park starting point for the component costs and that would help me out a lot :)

Only do it, if you'll let it be freely modifiable please :)

And the sugar-coating would be if it was done in an open-sourced design package :)

Simon
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techpaul
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Re: Please design a Primary School Board

Sun Aug 19, 2012 10:43 pm

Reread my comments about things not working.

You appear to be only readng the bits you like to read and skip the rest
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Re: Please design a Primary School Board

Sun Aug 19, 2012 10:48 pm

My circuit design would have a lot of Surface Mount components that are not available as DIP components, do you have surface mount assembly capability?

How much circuit knowledge do you have ?

Electronics deisgn is not quite the same as adding a software function.
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simplesi
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Re: Please design a Primary School Board

Sun Aug 19, 2012 11:02 pm

Well, an SM design wouldn't be my first choice but then again it might if the PCB was made with the SM components already on it and the schoos parents/local geeks just had to add the discrete components and it turned out cheaper than a non-SM version :)

My recent circuit design/soldering has been at Arduino level - I'm an ex RF broadcast engineer so if if the main circuit component runs on less than 20KV and costs less than £10K I am a bit out of my comfort zone :)

Simon
PS I do read everything but am trying to stick to the circuit design/electronic issues as much as possible :)
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jackokring
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Re: Please design a Primary School Board

Sun Aug 19, 2012 11:12 pm

For primary level, I'd suggest a bus/grid topology. Each device such as a motor, has it's full contained electrics, and has 3 connectors. What's on the connectors should not be important at this level, just that the device is seen, and becomes programmable. 3*4way socketing should be ok. Then there's the protocol. Fat Universal Serial Bus?

Cheers Jacko
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simplesi
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Re: Please design a Primary School Board

Sun Aug 19, 2012 11:20 pm

For primary level, I'd suggest a bus/grid topology. Each device such as a motor, has it's full contained electrics, and has 3 connectors.
Its like taking the littlebits devices a step further - nice idea:)
We've got a fair bit of kit (bulbs/leds/switches/motors/sensors etc) in primary schools already so a little I/O box would prob be more cost-effective (and maybe would teach about stuff at a more fundamental level?)
Simon
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jamesh
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Re: Please design a Primary School Board

Mon Aug 20, 2012 12:58 am

simplesi wrote:Well, an SM design wouldn't be my first choice but then again it might if the PCB was made with the SM components already on it and the schoos parents/local geeks just had to add the discrete components and it turned out cheaper than a non-SM version :)

My recent circuit design/soldering has been at Arduino level - I'm an ex RF broadcast engineer so if if the main circuit component runs on less than 20KV and costs less than £10K I am a bit out of my comfort zone :)

Simon
PS I do read everything but am trying to stick to the circuit design/electronic issues as much as possible :)
The Gertboard was designed in a couple of days. It then took weeks to get a PCB made and populated. It then had to be redesigned because of problems.

That's why 'just need a circuit and need it now' is *not* going to get you what you want. Your timescale is too short to do it.
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simplesi
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Re: Please design a Primary School Board

Mon Aug 20, 2012 1:19 am

:)
Well the one great solution would be a mini-Gertboard without the leds/jumpers etc but with an extra motor driver (and using a cheaper H Bridge to just drive smaller motors if possible) :)

BTW If you start at the beginning of the thread and look at my repeated "I just want a circuit :) " you'll realise that I was just attempting to keep the subject focused on a circuit schematic in the face of - you don't know what your asking for/have you seen this other thing type posts (from my point of view anyway) :)

I'd hoped there would be a few people around here (not busy with other things people) who might fancy a little project :)

And as an ex-operational engineer, - "can't be done in the timescale" - wasn't in our dictionary :)

I've managed to get 16 year olds interested in giving this a go on via twitter but I think its a job for the grown-ups (e.g several years designing/building stuff) :)

I think this thread has run its course and failed - so I'll try again tomorrow (today now) with a "who fancies designing a mini-Gertboard" :)

Thanks for your interest though :)

Simon
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techpaul
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Re: Please design a Primary School Board

Mon Aug 20, 2012 1:44 am

Forgetting motors for the moment as you really are not sure what you want on that front.

I could get you by end of week, a prototyping board with circuit schematic, no software as of yet with 16 bit GPIO and 4 x 0-5V Analog input. You add other bits externally. That is an assembled board with some testing done.

You can start with GPIO and analog inputs, the signal conditioning down to 0-5V range is your problem as you have not stated what types of sensors you are going to be connecting, how fast an update speed you need.

You can then add the motor control circuit of your choice if you wish. Motor control is a whole other board game and needs more time to consider things like stall current and control mechanisms, so that things dont get too hot and have some form of speed control unless binary on/off is OK.

If I get time in a few weeks I can look at motor control, when you can tell if you have any motors and what they are.

All software you generate is published and I get a copy.

This is a one time offer, for board at cost of parts and shipping as most parts already got in small quantities.
You can have a full BOM as well with RS/Farnell part numbers.

After this week I am on holiday and I will be shot hung drawn and quartered, boiled alive and as a minor nuanace castrated if I dont stop work for that week. Having been working 7 days a week for the last two months.
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Re: Please design a Primary School Board

Mon Aug 20, 2012 2:12 am

I will need to know by end of Tuesday btw as one componet needs to be sourced, if required.
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Re: Please design a Primary School Board

Mon Aug 20, 2012 6:09 am

techpaul wrote:cannot put my finger on the current at moment
Don't blame you it would make anyones eyes water ;)
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Re: Please design a Primary School Board

Mon Aug 20, 2012 8:29 am

Jim JKla wrote:
techpaul wrote:cannot put my finger on the current at moment
Don't blame you it would make anyones eyes water ;)
Actually I see the funny side of that, but the reasons are so they cannot make their eyes water or create sufficient spark energy to start fire easily from bench supplies.

However shorting out one AA battery makes a very hot battery and often melted wires :P
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simplesi
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Re: Please design a Primary School Board

Mon Aug 20, 2012 8:52 am

@techpaul
Thanks for your offer but unfortunately its really not what I'm although I can see that it is one way to eventually get there :)

I think I'll go down the route of seeing if we can put together bits and pieces from the Gertboard schematics and get something going along those lines :)

Thanks for pointing out some of the potential pitfalls with a design of this nature though and please come along and offer some advice when we get a circuit up.

Could you (or anyone) recommend a freeware circuit diagram drawing prog?

regards
Simon
Seeking help with Scratch and I/O stuff for Primary age children
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techpaul
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Re: Please design a Primary School Board

Mon Aug 20, 2012 9:14 am

Eagle lite allows 2 layer 100mm x 100mm board designs

This is the Free version for Windows/Linux/Mac

www.cadsoft.de

No I have not yet tried to install on Pi, but I doubt it is compiled for Arm
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simplesi
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Re: Please design a Primary School Board

Mon Aug 20, 2012 9:24 am

Ta
Don't think I'll be trying to run it the on RPi but it would an interesting exercise in its own right :)
Simon
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Re: Please design a Primary School Board

Mon Aug 20, 2012 9:44 am

/
simplesi wrote::)
And as an ex-operational engineer, - "can't be done in the timescale" - wasn't in our dictionary :)
Was not giving a good enough spec to actually do what is asked in your dictionary?
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simplesi
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Re: Please design a Primary School Board

Mon Aug 20, 2012 10:25 am

I tell you what, how about the next time I ask for something on the forums, we take it as read that what I'm asking for is daft and anyone is free to PM me on my daftness but that we try and stick to the forum subject on the forum? :)
Simon

PS
I hope that everyone can see the benefit of an open I/O expansion board tailored to primary age children and I hope that some of those fancy giving it a go just step forward to join in with the concept :)

At the end of the day, it might well be that we'll have to package up a Gertboard in a bigger case that won't look as cute and cuddly as http://sketchup.google.com/3dwarehouse/ ... revstart=0 and costs about £45 in total.

But I think its possible to do a bit better than that :)
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Jim JKla
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Re: Please design a Primary School Board

Mon Aug 20, 2012 11:21 am

simplesi
I was the first to reply to your original post and I did not think it was Daft but I did think it was Draft and an open question/request that was valid and posibly needed some qualification.

I still think it's a good idea that has some development potential.

I have also quickly concluded your case design is a grade 1 reprap makerspace project.

The whole thing may need some project management but it is well within the bounds of this community.

The Gertboard has it's place and will do what you want but there has to be room for a simpler cheaper solution.

If the Gertboard is the Black Forest Gateau you want the Victoria Sponge Cake either way I am shure there will be Cake. ;)
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