Author Topic: Hardware ideas  (Read 11556 times)

Offline awhaley

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Re: Hardware ideas
« Reply #30 on: February 15, 2009, »
I ordered the parts to put together a tester a while back too, but have been too focused on my dimmer system to get it all thrown together.

I'm planning on using a PIC16F722.  I DID order 3 cheap rotary encoders, but I think for my first pass, I'm going to use button up and button down on each digit... total of six buttons(Seems like the fastest channel select method.  Buttons could be multiplexed, but I'm not really that worried about running out of IO pins in this design).  I've got a slide pot that I'm planning to adc in for the level, and a three segment green led numeric display for output.

All the functionality I was planning was select a channel and the adc level gets spit out on it, with everything else at 0.

After watching this thread... I've got 5 IO lines that aren't in use yet... so that's 5 more buttons without messing with multi-plexing...


So I think I'll add (in version 0.2) :

1.  Send the codes to program one of RJ's devices to this channel
2.  Everything at 25%
3.  Test sequence - .5 second up, then .5 second down on each channel between 0 and the currently selected channel (so I don't have to wait for 400 empty channels to flash if I don't have that many channels in use) with a new channel starting up as the previous channel hits full (every .5 seconds)  If current channel is 1, test sequence will test all 512 channels.  Pressing test sequence again will cancel test.

and in version .3 :P
4.  Capture and release mode - Pressing this key means that each channel that is brought up will stay up until it is brought down... so you can bring up a channel, then dial to another channel, move the slider to a new level (or just wiggle it to 'grab' the channel if you want it at the same level as the one before)   Pressing the key again will release all the channels you've 'captured' this way.  In my release version, due to memory constraints you'd probably only be able to 'capture' 32 channels at one time...  but this is still enough to build a reasonable static look during testing...  And the 16F722 is pin compatible with some 18F series parts with enough ram to store a whole DMX packet, so you could just drop in one of those if you want the ability to capture 512 channels... and kick the firmware around a bit.  (the other fix, if people thought grabbing more channels was more important than being able to set dimmed levels for them... I could use 64 bytes to do a 'bitmap' of 512 channels for off and on control only in capture and release mode...?  I'd love thoughts on whether grabbing 32 channels and setting levels dynamically or being able to turn on and off 512 channels and have them latch till you hit release would be more useful to people?)

and I suppose from there, if you DID go to a chip with more storage and wanted to mutiplex the last input, you could add a couple of 'preset' buttons and a 'record' button to store the current look into the preset buttons, for quick recall later?  I'll lose interest in the project before that happens, but someone else could hack it in.  :)

I'm at least a month away from really getting into all this, and it sounds like others are working on it too, so I posted my plans in case anyone wants to pillage ideas from them.  I probably will be building my tester, because I want to learn what it has to teach as a project, but if someone in the DIY community comes up with a solution first, great!  :)

Art

Offline RPM

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Re: Hardware ideas
« Reply #31 on: February 15, 2009, »
Mike,

Looks good, but wouldn't the R1/C1 time constant combination cause problems with ICSP programming?
From what I remember, doesn't Atmel specifiy using just a 10K resistor on the reset line if the ICSP is used.


  Robert



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I just threw this schematic together.  It's still missing the power supply - any ideas?
/mike


Offline n1ist

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Re: Hardware ideas
« Reply #32 on: February 16, 2009, »
The AVRISP MK2 docs recommend no smaller than 4k7.  Looking around, I see people are using either 4k7 or 10k resistors for the reset pullup.  The time constant shouldn't matter for in-circuit programming as reset is held low for the entire program cycle.   As long as the programmer can pull it down, it should be OK. 

I have always used 4k75 and haven't had a reset problem (I have about 20K boards with various Atmel processors out in the field).  One thing that I have learned is to always use the built-in brownout detector as otherwise the EEPROM can get corrupted.  Oh, and you can't enable those fuses from firmware, only from the ISP pod - it gets tiring updating 800 ATMega3250s around the outside of a 3M tall, 3M diameter tester...

For power, I'm looking at using 3 AA cells feeding a boost converter, likely an LM2735X.


Offline ThaiWay

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Re: Hardware ideas
« Reply #33 on: February 16, 2009, »
This is all way above my head... but i'm glad you guys are working on it!

John
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John

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Offline RPM

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Re: Hardware ideas
« Reply #34 on: February 16, 2009, »
I like the idea of using 3AA cells with the LM2735, but that would drive the parts cost up and the LM2735 I believe is only available in surface mount.

I was just going to use a 9v battery with a plain old 7805 regulator... cheap and simple.

 Robert

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The AVRISP MK2 docs recommend no smaller than 4k7.  Looking around, I see people are using either 4k7 or 10k resistors for the reset pullup.  The time constant shouldn't matter for in-circuit programming as reset is held low for the entire program cycle.   As long as the programmer can pull it down, it should be OK. 

I have always used 4k75 and haven't had a reset problem (I have about 20K boards with various Atmel processors out in the field).  One thing that I have learned is to always use the built-in brownout detector as otherwise the EEPROM can get corrupted.  Oh, and you can't enable those fuses from firmware, only from the ISP pod - it gets tiring updating 800 ATMega3250s around the outside of a 3M tall, 3M diameter tester...

For power, I'm looking at using 3 AA cells feeding a boost converter, likely an LM2735X.



Offline dmaccole

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Re: Hardware ideas
« Reply #35 on: February 17, 2009, »
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I was just going to use a 9v battery with a plain old 7805 regulator... cheap and simple.
I'm not criticizing this idea, but am merely using it as a jumping-off point for ranting:

Have you priced 9v batteries recently!?! They are $5! If not more!

I only use them for breadboard testing of my humble little projects, so I had been happy buying them for $1 at the Dollar Store; when DS ran out a few months back, I started looking around for alternate supplies: RS, drug stores, HD, L, etc. Five bucks. Jeeze.

Rant ended. ;) ... Sorry for the OT.

\dmc
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Offline n1ist

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Re: Hardware ideas
« Reply #36 on: February 17, 2009, »
That and you will be wasting half of their capacity heating the regulator.  If you don't want to deal with a switcher, use 4 nicads in series to get 5V, or 4 alkalines in series with a dropping diode.

Surface mount isn't too hard to deal with.  The SOT-23 that the LM2735 comes in actually has a wider spacing than the TQFP-44 of the processor.

Here's the board so far; I still need to add the bypass caps and the reset parts.
/mike

Offline RPM

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Re: Hardware ideas
« Reply #37 on: February 17, 2009, »
I appreciate the input.

I agree... those 9V batteries can get pricey.  I would probably use AA cells just because of this, since you can get a brick of 30-40 of them for around $10.  I guess my point was that it would need to be a simple circuit to keep cost down and be easy to build, with only DIP IC's.

  Robert


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I was just going to use a 9v battery with a plain old 7805 regulator... cheap and simple.
I'm not criticizing this idea, but am merely using it as a jumping-off point for ranting:

Have you priced 9v batteries recently!?! They are $5! If not more!

I only use them for breadboard testing of my humble little projects, so I had been happy buying them for $1 at the Dollar Store; when DS ran out a few months back, I started looking around for alternate supplies: RS, drug stores, HD, L, etc. Five bucks. Jeeze.

Rant ended. ;) ... Sorry for the OT.

\dmc


Offline vairmoose

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Re: Hardware ideas
« Reply #38 on: February 17, 2009, »
Mike,   Is your tester PCB size and mounting based on a particular enclosure?   

Larry
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Offline softshelpro

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Re: Hardware ideas
« Reply #39 on: December 12, 2009, »
What's the status of this toy?
There are two types of people in this world, those who are Dorks and those who are in denial.