Junebug help??

be80be · May 25, 2009

You sure you burned up the pic and not something else. You can burn them up but easy if you wire the gnd to VDD . Put you a Schottky Barrier Rectifiers On VDD to keep that from happening.

blueroomelectronics · May 25, 2009

That's why people put diodes in powersupply inputs. A neat trick (no voltage drop) is a crowbar diode and PTC fuse

be80be · May 25, 2009

Here a good link about protection solutions **broken link removed**
And here some on crowbar diodes https://en.wikibooks.org/wiki/Practical_Electronics/Crowbar_circuit

MrDEB · May 26, 2009

now you tell me!!

the horses are out and the barn door is still open.
never occured to me to put a diode in line to prevent backwards polarity or ??
being this is battery powered.
the unit for the automobile will have the crowbar circuit.
anything w/ less parts?? as I have 3 boards (battery powered for use n garden).battery powered only4.5v, no LM386.
perhaps I just don't include on the 3 etched boards but add to design.

MrDEB · May 26, 2009

suggestions for SCR and schotky

pic of LDO regulator and crowbar
need suggestions for scr and schottky diode
output is 5v max, 100-150ma if you count the LM386 (I need the 12v for the amp to avoid clipping)
the speaker is .3w so not to big of amp is needed.

3v0 · May 26, 2009

I would like an EE type to look this over and see if it has any merit. I COULD BE WRONG.

A while back we talked about using regulators designed for use with cars. They will take care of reverse and over voltage problems.

I would use a LM2931 to power the 5V side which I think is just the PIC. Is is made for automotive use with protection from over voltage and being hooked up backward.

You need protection for the amp which is 12V. 12V automotive grade regulators are a bit harder to find and may be more expensive. You have to put in the time to look for them. I found NCV8674DS120G

Features
• 5.0 V and 12 V Output Voltage Options
• 2.0% Output Accuracy, Over Full Temperature Range
• 40 A Maximum Quiescent Current at IOUT = 100 A
• 600 mV Maximum Dropout Voltage at 350 mA Load Current
• Wide Input Voltage Operating Range of 5.5 V to 45 V
• Internal Fault Protection
♦ −42 V Reverse Voltage
♦ Short Circuit/Overcurrent
♦ Thermal Overload
• NCV Prefix for Automotive and Other Applications Requiring Site
and Control Changes
• AEC−Q100 Qualified
• EMC Compliant
• This is a Pb−Free Device

In short start with automotive grade regulators then add fuses as needed.

MrDEB · May 26, 2009

the LM2937 is for automotive

https://www.electro-tech-online.com/custompdfs/2009/05/LM2937-1.pdf
they both look about the same??
the LM386 - I could just put a zener to limit the voltage, say 12v or less.
not real concerned about the amp as I am the PIC
the LM386 I think will take up to 18v.
the LM2937 was the part that was discussed last week??

3v0 · May 26, 2009

When I looked at the datasheet very early this AM the National datasheet for the LM2937 did not load. The datasheet for the clone I looked at did not show that it had LOAD dump etc. It will work.

But it is about 3X more then you need for the PIC. The little TO-92 (think transistor) 100mA LM2931 will work fine to power the PIC.

I would like to see the amp with more protection then a zener. If you could find the 12V auto style regulators at the right price it would be a safer bet. Thinking here is that the more units you sell the more possible one or more will be exposed to a car that will ruin them. Maybe a zener is OK. I will defer to the EE's, I could be over cautious.

Then there is the deal with hooking it up backwards. A diode to block the current when backwards would fix that for the amp. For the PIC the regulator handles the problem.

be80be · May 26, 2009

Take a look at this

And here is where it's at on the form https://www.electro-tech-online.com/threads/regulated-12vdc-from-car.91800/
Hero999 said

There's nothing wrong with the home made schematic.

Just make sure the BJT and MOSFET are good enough for 100V.

Adding a zener between the gate and source of the MOSFET will also help to make it more robust.

A 15V zener across the output terminals will also help protect the device connected to it.

Current limiting can be received by adding a couple of transistors (at the expense of adding about 600mV on the to the drop-out) or a polyfuse (assuming the MOSFET can take the surge for long enough for the polyfuse to protect it).

3v0 · May 26, 2009

Yes and you can buy a regulator designed to work in a cars electrical system for between 25 cents and $2.50 or so.

This is the same POS as last time. Bill brings up a subject with a one liner and you flesh it out without regard to if it is a good idea or not.

I asked for an EE opinion and said I COULD BE WRONG.

The Fourm is yours BE. Sorry for the intrusion.

MrDEB · May 26, 2009

be80be · May 26, 2009

Mr Deb for what your doing any thing would work a zener diode to clamp the 12 volts and any good 5 volt reg . Now if it was going in space on the shuttle Get you a EE to draw it up for you If you keep on like your doing some one in china will be selling it before you. I would really like to see you in that New BMW.

be80be · May 26, 2009

That's you

This is the same POS as last time. Bill brings up a subject with a one liner and you flesh it out without regard to if it is a good idea or not.

this is you

A while back we talked about using regulators designed for use with cars. They will take care of reverse and over voltage problems.

And what I posted came from your A while back we talked about using regulators designed for use with cars

MrDEB · May 26, 2009

for cost etc I am going with

the 5v LDO reg. and a 7812 for the 12v side.
trying to look at cost.
unless something better comes along.
have boards etched and drilled for 3 units.
have several homeowners interested in testing.
just need to solder up the boards as well as the proto-type unit (need to reconfigure the battery power packs so I don't blow another PIC (have polarized plugs for rest of units)
will be testing tomorrow (I know several fields where deer hang out all day).
then turn it on near some cows (just to be sure they are not bothered by unit.)
If all goes as planed I will start selling by next week.
future units to be SMD after seeing several ways to solder SMDs EASY

MrDEB · May 26, 2009

oh yea the BMW

thinking a VW the new one they are advertising that gets 58mpg.

MrDEB · May 27, 2009

why 2 regulators??

see the forest w/ trees
why 2 regulators when the 12v unit is a LDO type for the amp and a 5v for the PIC?
why not just one regulator (amp) and a zener / transistor circuit for the 5v PIC
but use a 4.3 zener for a little leeway on the voltage.
not like the PIC needs alot of current.
cheaper and very few parts.
I am not contemplating on building a-lot of units unless there is a demand (build as needed / ordered).
IF I get a big demand for units then yes I will buy in large quantities and thus cheaper per unit.
not even sure if this circuit would fly?????
just thinking why not??

Pommie · May 27, 2009

If you want your batteries to last then use a 5V switching regulator that is efficient. Do not use the half supply idea. It will just flatten half the batteries first. Do not even contemplate a zener as that is the most inefficient regulator going.

If you are going to try and sell this device then you have to assume that you will sell at least 1000. At $30 each that will give you (my guess) 1-2 months wages. I based that on 50% profit (optimistic) and no advertising costs.

Seriously, if you want to make money off of this device then you need to find someone (company) with a foot in the market or be in a position where you can go many months without an income.

Mike.

3v0 · May 27, 2009

If I understand it right you want to use the unit on both cars and on a battery. The optimal regulation for each is different.

For a battery operated unit you want efficient regulation to make the battery last as long as possible. As suggested by Pommie a switching regulator is the most efficent. You could also increase the run time by turning the amp off between a few seconds of sound. Ground the amp with a FET controlled by the PIC. If you can do without the amp on this unit that changes things to.

Use on a car requires more elaborate protection in addition to regulation, efficiency is of little concern (other then heat). The 5V regulator is 18 cents so using two regulator is not an issue.

MrDEB · May 27, 2009

TWO different designs and power supplies

the unit for cars is w/ amp, needs 12v for amp and 5v for PIC
the unit needs the LDO regulators etc.
the unit for home use has a PIR, runs on 3 AAA batteries so no regulator is needed.the amp is not needed. Just a 2n2222 drives the .2w speaker.
why a switching regulator?? the PIC is sleeping and the PIR wakes it up, runs for up to 50 seconds then shuts down.
problem is the automotive supply circuit which the PIC is running all the time the car is on

3v0 · May 27, 2009

You only need 100mA to run the PIC.

In the schematic for the car the AMP is unprotected, and the amp is connected to the PIC.

me said:
Use on a car requires more elaborate protection in addition to regulation, efficiency is of little concern (other then heat). The 5V regulator is 18 cents so using two regulator is not an issue.

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