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IamSmooth

Mon Jan 25 2010, 08:09PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

I am not sure I will do this, but I would like to know what it involves. Right now I am using a PLL to lock onto the resonant frequency for an induction heater. However, it still requires that I have the PLL in the correct range, and it still requires slight tweeking during use.

If I change the coil, or put different metals in the coil, the resonant frequency can be so far off that it requires readjustment of the PLL. It would be nice if I had a chip running a simple software routine that started pulsing the driver above resonance and then decreased the frequency. As the frequency is changed it could look at inverter current, or I could XOR the inverter voltage and current looking for the region where current goes from lagging to leading.

My initial questions are:
what chip could be programmed to do this?
what auxillary equipment do I need to program the chip?
what language is being used for the programming?

Nicko

Mon Jan 25 2010, 08:55PM

Registered Member #1334 Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615

Small PIC or AVR would do the job simply - there are some really tiny ones that are dead cheap but quite tricky to program (cos they're small). Best to go for something in a DIP8 package and socket it (avoid SMDs). You need a few I/O pins and probably some analogue input (D/A converter). Most have PWM & Timers, even in the 8-pin versions...

Programming is either in assembler, C or BASIC-type languages. The very very small uPs don;t have a stack, which makes the use of high-level languages tricky, so sometimes its worth paying the extra buck or two just so you can use BASIC or C (or whatever). Arduinos etc. would be very much overkill for this.

Programming depends on the uP - some can be done via a simple serial/parallel port adapter - if you have a few quid, buy a decent programmer - some are very cheap.

Olimex do a whole bunch of development boards etc. for the experimenter - I think that Sparkfun might be agents in the USA. There are a zillion boards available anyway...

Advantage of using a BASIC-type language is that its simple to learn and often will hide the unpleasantness of the hardware from you - if you've not messed with uPs much, frigging around with A/D converters etc. can be a pain.

Have a look at

- the author is a good guy and I know lots of people who use his stuff with great success.

If you consider the AVR route (which are my favourites), there is a really useful forum at

.

Both PICs and AVRs have free IDEs from the manufacturer, and if you want to do your own thing in an HLL, you can use WinAVR for the AVR (an AVR port of the GNU C tool chain) and similar for the PICs. As I don;t use PICs any more, someone else will no doubt leap in here.

One thing I would say is that uPs and BIG CURRENTS do NOT mix well. Many will lose the plot completely unless very well shielded (and that means everything the has anything to do with the uP shielded).

HTH

IamSmooth

Wed Jan 27 2010, 06:41AM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567

Would ATMEL be a good company to get some PLCs from?

Bjørn

Wed Jan 27 2010, 07:05AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Use something someone else uses and make sure they will reply to your questions then you can't go far wrong. It will save you a lot of time.

It does not really matter what you use as long as you don't try to use a chip that is not really powerful enough for the job. Atmel will be fine, they got the full range from simple 8 bit to powerful 32 bit microcontrollers that can do just about anything.

IamSmooth

Wed Jan 27 2010, 07:38AM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

I take it that you have used their chips?

Nicko

Wed Jan 27 2010, 08:42AM

Registered Member #1334 Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615

IamSmooth wrote ...

Would ATMEL be a good company to get some PLCs from?

Atmel don't do PLCs - they do micro processors and some support chips - PLCs are build on uPs, typically 8051 or similar based with added output relays and opto-isolated analogue & digital inputs. They tend to use a deterministic flow-chart type language that is interpreted by the underlying uP software and which abstracts the physical implementation of the hardware. So, instead of worrying about bits in an I/O register, you might have pseudo-code such as "if analog-input-1 > 3.5V then close relay-2" (sort of!).

Join the AVR Freaks forum and ask there - lots of helpful people.

Bjørn

Thu Jan 28 2010, 06:37AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

A programmable logic controller (PLC) is an expensive device generally used when you make good money from what you make. You are most likely looking for a microcontroller that is much more stripped down and can cost down to almost nothing.

I have used most types of microprocessors and microcontrollers one time or another. When I am experimenting with something I use 32 bit ARM chips because it does not make sense to waste a lot of time just to save $10 a year. If I make something that is supposed to be used for a long time and an ARM chip seems too much I use a PIC for historical reasons (I got a PIC development kit for cheap).

In the chat room you will find users of most microcontrollers.

IamSmooth

Thu Jan 28 2010, 06:58AM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

Bjorn,

I'll go to the chat room next, but if I don't have a programmable controller, how do I program the chip?

My goal is for a one-time project so I don't want to spend a fortune. However, i would like it to work well, whatever route I choose.

Bjørn

Thu Jan 28 2010, 07:37AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Today many chips come programmed with boot loaders that makes it possible to connect them more or less directly to a PC over RS-232 or USB. In some cases it is like that from the manufacturer or it can be done by a reseller that will sell those chips for a slightly higher price.

The other option is to build your own programmer that can be a s simple as a few resistors even if a bootloader is generally a more reliable method.

Steve Conner

Thu Jan 28 2010, 09:35AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

If you're a uC newbie, you could do worse than to check out the Arduino.

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