TineFPGA-GOLD Metal detector

[SaltyDog]

Quote:"@Skippy, you are mostly correct"
What's with the 'mostly' ? Did you read my note about synchronous rectifiers, using power FET's the 'wrong way' round ? And if you're using it the 'wrong way', it doesn't matter if there's a diode internal to the FET or not.
.

Because you are completely wrong!

Mosfets when they are driven into conduction can pass current in "both" directions drain to source!!! It does matter if there is a body diode because obviously if you have a negative voltage on the drain in the "off" state the diode will still conduct.

There are a number of small signal mosfet's that DON'T have body diodes ... and even some power mosfets can be had without them .. and i'm not just talking about SIC fet's or GaN fets ..

[dbanner]

Saltydog, pitty you missed the fact that Rext @1k limits the current to 20mA but won't work in a reverse polarity condition. After many decades in the game , it's nice to know that you can still blow things up.
I also noticed you tied the OE pin to ground, thus I assume will give full brightness as this pin is active low.? Seems like there is pwm possibility for % brightness maybe for future versions of your design.
I'm not sure how this is meant to work though.


Now relating to the issue of the power supply for the LED array, I suggested using the l5970d, since it is tailor made for this purpose, notwithstanding +12bat being circuit common. Might as well go full in on a modern design, if your design works as well as you claim, a 555 solution seems a bit archaic, less efficient.

[SaltyDog]

I also noticed you tied the OE pin to ground, thus I assume will give full brightness as this pin is active low.? Seems like there is pwm possibility for % brightness maybe for future versions of your design.



Now relating to the issue of the power supply for the LED array, I suggested using the l5970d, since it is tailor made for this purpose, notwithstanding +12bat being circuit common. Might as well go full in on a modern design, if your design works as well as you claim, a 555 solution seems a bit archaic, less efficient.

The OE pin only selects the device for SPI comms .... you do not get any current until you latch in a value via SPI and latch it with the LE line ..
(you can control brighness with the OE pin, but I am not using it that way)

I have decided that I will use an isolation chip like the one I suggested (ADum160N)to isolate the SPI lines, since it has 7 channels, I will use some of the remainder for the coil MOSFET drive and the speaker/phones driver .. it is a much cheaper alternative than another switcher power suppy.

(I am already using opto isolation for the coil MOSFET drive ... so I can remove that saving cost ..)

PS: According to the datasheet, The LED driver can supply 5-100 mA for each LED adjustable by Rext ..

[Skippy]

You're not paying much attention to what I've said are you.
"Mosfets when they are driven into conduction can pass current in "both" directions drain to source!!!"
I've already said that several times, please re-read.

"It does matter if there is a body diode because obviously if you have a negative voltage on the drain in the "off" state the diode will still conduct."
I was referring to the sychronous rectifier application, where the Drain-Source channel is doing all the conducting, and very little current will flow through the body diode that's in parallel with it, so it doesn't matter if it's present or not.

"There are a number of small signal mosfet's that don't have body diodes"
yes, I said that, I even quoted a part number, please re-read.

"... and even some power mosfets can be had without them"
so I ask again, can you please provide a part number for such a device, it would be useful to know.

[dbanner]

In this particular driver chip, seems the fets are sinking current at a constant rate limited by Rext. Is this correct? But sourceing current, we see the magic smoke.
Can someone describe the electrical circuit equivalent of how Rext is connected? Are these all common source fets with Rext connected in series, Just trying to grasp what actually happened.

[dbanner]

It is far better to use the pwm to control the brightness. The maximum brightness (100% mod.) would then be a function of Rext and Vc.
VCC for a single LED per output need only be 0.5 above LED voltage drop as stated in the datasheet.
Can you explain to me this aspect and why you wanted such a high supply (-12V)

[dbanner]

Lastly, do engineers normally have fist fights when they are in the same room at work? If so I'd better learn some Kung Fu.

[Searchy]

Did i get it right, that this project will stay a closed source and just wants free support/inspiration/debugging from experienced forum members?
Looking at the design/concept (10 bit ADC, 200kHz BW, -12V on outputs....) i am sceptical about the true potential of the implementation and the results (not shown/prooven) so far.
However... good promotion

[dbanner]

If you are a blind man trying to cross the street in order to sign big lucrative contract that awaits your signature, should I hold your hand and help you across or should I kick you in the teeth and push you out into the incoming traffic. It is quintessential dilemma.

Probably not applicable in this context but you can get the idea.

[WM6]

Did i get it right, that this project will stay a closed source and just wants free
support/inspiration/debugging from experienced forum members?

That's how it's read on all, now already 5 (mostly empty self-promo) pages of this tread.

But most probably such behavior is not in spirit of this forum, especially not in spirit of "Tech Forum".

Closed development, hidden from public, could be utterly OK, but then secret developer put himself,
(regarding promo), in range with other (trade secret maintaining) producer in MD business.
Their dedicated forum here is "Buy-Sell-Trade" part of this forum and not "Tech-Forum".

[waltr]

Lastly, do engineers normally have fist fights when they are in the same room at work? If so I'd better learn some Kung Fu.

Nearly at times.
Reason I took Conflict Resolution classes.

[6666]

Did i get it right, that this project will stay a closed source and just wants free support/inspiration/debugging from experienced forum members?
Looking at the design/concept (10 bit ADC, 200kHz BW, -12V on outputs....) i am sceptical about the true potential of the implementation and the results (not shown/prooven) so far.
However... good promotion

Its a private project, he will be selling kits, still interested in it but.

[Qiaozhi]

That's how it's read on all, now already 5 (mostly empty self-promo) pages of this tread.

But most probably such behavior is not in spirit of this forum, especially not in spirit of "Tech Forum".

Closed development, hidden from public, could be utterly OK, but then secret developer put himself,
(regarding promo), in range with other (trade secret maintaining) producer in MD business.
Their dedicated forum here is "Buy-Sell-Trade" part of this forum and not "Tech-Forum".

There is nothing wrong with wanting to develop a private project, as not all people want to share their hard work for free.

Unfortunately I may have made things worse with the Minipulse Plus and Geotech Baracuda projects, such that now everyone expects stuff to be provided for free and open-source. However, that's not all bad, as many others have taken the Minipulse Plus design and contributed to its improvement, such as adding a microcontroller, experimenting with ground balance and different preamps, and testing various audio options. Of course, that was the initial intention. Ivconic has also contributed designs for free. In particular, the popular TGSL and IGSL. Also, not forgetting Carl, who kicked off this free project idea with Hammerhead. Sorry, if I've missed out others who have freely given away their projects on Geotech. Maybe we're all to blame.

In the past we've seen the latest and greatest ideas hyped in the Tech Forum, only for the project to suddenly become very secretive with claims that it's going commercial. Then complete silence ... never to be heard of again.

As Carl aptly once put it:

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1. KEEP YER TRAP SHUT. Unless the project is a public effort, as many are here on Geotech. While premature public hyping doesn't necessarily break a project, it does incredible damage to the reputations of the design and the designer when things don't work out, as is the case 95% of the time.

2. Get help. Competent help. Preferably by someone who's been there done that. You can't do it all alone.

3. A day in the field is worth a month in the lab. Get it off the bench ASAP, you will quickly see whether that great idea is worth a crap.

4. Focus on the things that matter the most. Performance is #1. A talking detector is #1000. When you have the level of performance that will definitely sell, STOP THE DESIGN PROCESS and move on to making it producible. You'll get to implement that Next Great Idea in Version 2.

5. Forget about building detectors. Ain't gonna happen, at least on a scale that will pay the rent. Find someone else to do that. Again, someone who knows how. Also lets you move on to Version 2, which is more fun than potting coils all day.

6. Forget about patents. Unless you get the Partner Production Company (#5) to deal with them. That $5,000 patent ain't worth squat unless you've got the $100,000 to back it up.

7. Respect the competition. Like it or not, they are already successful, have lots of satisfied users, and are making lots of money. Focus on beating them with a better product, not with public displays of contempt. And never ever ever criticize a user of a competitor's product. That's one lost sale, or more.

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[6666]

Unfortunately I may have made things worse with the Minipulse Plus and Geotech Baracuda projects,

Not at all George your projects have been enjoyed by many people around the world.

[SaltyDog]

I will no longer be offering my kits to the trolls in this forum .... It will go on sale as a commercial product ...
You reap what you sow ..

Bye Bye