[TriEmbed] Need simple 1A controlled current power supply

[Rodney Radford]

It would be great to find a board like this that had the on/off control
pulled out so it can be controlled by the Arduino pin to turn on/off the
magnet coil.

That is the other part of the solution - not just 1A, but 1A I can pulse to
a specific pattern.

I know that part supports it, but all the boards appear to not support that
feature. It is possible to cut the lead to the part and pull out that one
pin, but I need something I can pass along to the students to build and I
like simplicity.

Have you seen any that have digital enable control, or an easy way to get
that? The price point for these boards is definitely in the range of what I
wanted to spend.

Thanx,
Rodney


On Mon, Sep 26, 2016 at 11:56 AM, Robert Gasiorowski <rgresume at gmail.com>
wrote:

> Here are couple of links for you. I use those for many things, it's
> cheaper than building your own. Ping me if you need one right away.
>
> http://www.ebay.com/itm/5pcs-Re-DC-DC-3A-Buck-Converter-
> Adjustable-Step-Down-Power-Supply-Module-LM2596S-/221991448900?hash=
> item33afb8b144:g:d5YAAOSwX~dWktJo
>
> http://www.ebay.com/itm/DC-DC-3A-Buck-Converter-Adjustable-
> Step-Down-Power-Supply-Module-LM2596S-/272254241762?var=&
> hash=item3f639e0be2:m:mQbDIu3F52Dp9nEA1AhO84A
>
> On Mon, Sep 26, 2016 at 11:24 AM, Rodney Radford <ncgadgetry at gmail.com>
> wrote:
>
>> Yes!  This is exactly the type of solution I was hoping to find.  I read
>> through several on/off regulator specs over the weekend, but did not find
>> one that could handle the 1A I needed (most were in the 100-200mA range).
>>
>> This is a good solution and pre-built boards with the necessary passive
>> components are under $4 on eBay/Amazon.  I will order one to try out, but
>> open to other suggestions as well.
>>
>> Thank you
>>
>> On Mon, Sep 26, 2016 at 10:21 AM, Robert Gasiorowski <rgresume at gmail.com>
>> wrote:
>>
>>> Can I suggest LM2576 based switcher? There are plenty of them on eBay
>>> for $1-$1.25.
>>> You can feed them 12V and get 1.25V @ 3A. Then use resistor if you need
>>> even lower voltage.
>>>
>>> Rob.
>>>
>>> On Mon, Sep 26, 2016 at 8:29 AM, Rodney Radford via TriEmbed <
>>> triembed at triembed.org> wrote:
>>>
>>>> For the Southeastcon 2017 hardware robotics competition, one of the
>>>> requirements is to be able to switch on and off a magnet field.
>>>>
>>>> The field is defined as number of turns, diameter, core, and the
>>>> current - 1A - through it.  I need a simple (and cheap) way to implement
>>>> this.  I will be building 8x of these for the competition and each school
>>>> will be building one for their trial runs, so keeping it cheap and simple
>>>> is better than elegant and higher cost.
>>>>
>>>> Initially I was planning on a very simple solution - a MOSFET switching
>>>> current to the coil in series with a power resistor to drop the voltage.
>>>> At first this was a 5 ohm, 5W power resistor (since the coil is below 0.1
>>>> ohm), but then that changed to a 12 ohm, 12W power resistor as I switched
>>>> over to using 12v to power everything since I needed that for the relays
>>>> anyway (for another part of the design).
>>>>
>>>> This works, and is cheap and easy to build and if the coil is only on
>>>> for a few seconds at a time, this is a great solution. However, a change in
>>>> the contest stated that the coil is initially powered on (so robots can use
>>>> it to navigate to the coil) and if the robot fails, it could be on for the
>>>> full duration of the 5 minute competition.
>>>>
>>>> I tested this last night and it does work, but 12w through even a metal
>>>> power resistor is HOT after about 30 seconds.  I would hate to use this for
>>>> 5 minutes.  The cost is good - below $2 for the MOSFET and power resistor -
>>>> but I am looking to see if there is a better solution.
>>>>
>>>> Some ideas considered:
>>>> * use a lower voltage - would work, but I would need a lower voltage 1A
>>>> supply
>>>> * use a switched regulator - get the lower voltage *and* ability to
>>>> control it
>>>> * others?
>>>>
>>>> Any thoughts / suggestions?
>>>>
>>>> Btw, I will be bringing this in to the next meeting (next R&A/TAR and
>>>> next Triembed) to show the progress on the hardware and software design.
>>>> Most of it is done now and I hope to finish it in the next few days.
>>>>
>>>> On another issue - I watched a couple Eagle videos this weekend and was
>>>> able to complete the schematic capture for the board and even routed a PCB.
>>>> The routes were done with the auto-router and they were ugly, but
>>>> functional. Not sure if I will just route it myself, or route some and let
>>>> the autorouter finish, etc, but I need to investigate the design rules for
>>>> the fab house first to verify I have spacings, hole sizes, trace widths,
>>>> etc are correct before I dump too much more time into it.
>>>>
>>>> Thanx,
>>>> Rodney
>>>>
>>>>
>>>> _______________________________________________
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>>>>
>>>>
>>>
>>
>
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