Baracuda Build (silverdog kit Rev2)

[Qiaozhi]

Haven't read every post so my have missed something but my offset cermet is 25K

The PCB shows the value as 25k, but the original schematic shows 100k. Impulses's board has a 20k installed.

Possibly connected to pin 7 ? and +-5V and a 270K resistor on pin one

That's the way the PCB is wired. It works, but it's not the recommended method to use.
I intend to use the offset null method shown in the datasheet.

@Q, It looks perfect... 40106 and 5534 look perfect and the power supply makes sense at last...

@Koala, the schematic connects the 5534 as per the datasheet... all other schematics deviated for some unknown reason...

I'll breadboard it tomorrow and see if I can spot any issues... hope I can find enough empty breadboard ... looking forward to it...
Mike

I'll wait until you've confirmed the changes before starting the PCB layout. My intention is to keep component placement similar to the original. Otherwise, if we make too many changes, it will cease to a Baracuda.

If you look at the data sheet r21 should go to pin 7 and the voltage on pin 7 (which should be/is +5v) used for off set, not batt gnd

http://circuits.datasheetdir.com/25/...4-circuits.jpg

Well spotted. That was my mistake, and the 22k resistor should be connected to +5V.

Q won't the 7660 still be in trouble with 12 volts applied? Maybe just specify the 7660A or a 7662 and/or add a diode in series with the supply.

The schematic is just showing a generic 7660, and the parts list will specify a 7660A. I'll change the component name to 7660A on the schematic to avoid confusion, unless we add FatBob's modification below.

On My Bara I knew the 12V was going to be a problem so I added a LDO set to 9V.

3 Lipo's input will range from 12V - 9V roughly and the LDO works with 300 mv differance.
I have a lot of MAX667's so I used that for mine.

At the same time I increased the supplies to +-9V for a little more headroom. I haven't tried this
yet as I'm finishing up my Surf just now.

[ATTACH]35886[/ATTACH]

This might be a good modification to add to the Baracuda, as it would allow any version of the 7660 to be used. It looks like the original design is intended to use a battery pack with a nominal 9V (i.e. 6x 1.5V AA cells), but many constructors see the maximum voltage listed as 12V, and then connect a 12V battery pack, which eventually damages the 7660A,

A corrected schematic will be uploaded soon.

[FatBob]

On My Bara I knew the 12V was going to be a problem so I added a LDO set to 9V.

3 Lipo's input will range from 12V - 9V roughly and the LDO works with 300 mv differance.
I have a lot of MAX667's so I used that for mine.

At the same time I increased the supplies to +-9V for a little more headroom. I haven't tried this
yet as I'm finishing up my Surf just now.

[Old cart]

Please check over the preliminary schematic for a corrected version of the Baracuda (see PDF attachment).
See if you can spot any errors, or anything I've missed.

Q won't the 7660 still be in trouble with 12 volts applied? Maybe just specify the 7660A or a 7662 and/or add a diode in series with the supply.

[6666]

If you look at the data sheet r21 should go to pin 7 and the voltage on pin 7 (which should be/is +5v) used for off set, not batt gnd

http://circuits.datasheetdir.com/25/...4-circuits.jpg

[Michaelo]

@Q, It looks perfect... 40106 and 5534 look perfect and the power supply makes sense at last...

@Koala, the schematic connects the 5534 as per the datasheet... all other schematics deviated for some unknown reason...

I'll breadboard it tomorrow and see if I can spot any issues... hope I can find enough empty breadboard ... looking forward to it...
Mike

[Koala]

Possibly connected to pin 7 ? and +-5V and a 270K resistor on pin one

[Koala]

Haven't read every post so my have missed something but my offset cermet is 25K

[Qiaozhi]

Preliminary schematic

Please check over the preliminary schematic for a corrected version of the Baracuda (see PDF attachment).
See if you can spot any errors, or anything I've missed.

[Koala]

https://www.youtube.com/watch?v=_Lw36Akol-Q

Is this a valid test ?


https://www.youtube.com/watch?v=LR0fEvhhV5g


Quick view of board

[Koala]

Thats a good result for an 8" coil.It calcs to about 490uH.

Measured at 450uH with a cheap component tester. (£10.10)

~

Don't know how accurate it is on inductance but every resistor/capacitor I have thrown at it have been bang on.

Also used it to match the FETs

[6666]

Coil is about 8.5" and 29 turns of .71mm copper enamelled wire.

Just over 12" on a one pound coin.

Thats a good result for an 8" coil.It calcs to about 490uH.

[6666]

I've just complete breadboarding the design and tested the code... works a treat.

Looks interesting thanks
the delay between the first and second sample is more like up to 200uS

[Michaelo]

Looks like everything is sorted... looking forward to Qiaozhi's new schematic...

A word on the Bara Pulse Tool (for anyone interested)...
I've just complete breadboarding the design and tested the code... works a treat....
Only remains to write the code for the four keys so I can modify the pulse timing (and delays between them) on the fly, in the mean time I'm using the default timing.

I'm working under the assumption the the default timing is as follows... (correct me if I'm wrong)...

• TX Pulse Width: 100uS
• Delay before main sample pulse 10-60uS adjustable...
• Main sample pulse and second sample widths are both 45uS...
• The delay between the main sample and second sample is about 80-100us (adjustable)...
• Duty cycle ~640 (pps) (also modifiable)...

Pulses can be changed in 1uS intervals...
The output pulses are level shifted and buffered (using 4049 and 40106)....
My test unit is powered from four lithium ion batteries (4 x 3.7 volts) in series to provides a common ground making the design considerably easier...
Although the unit only requires 5 volts, I have also added a -5 volt regulator to allow level shifting to 10 volts...
This allow powering the unit from the same supply as the bara (you need the positive, negative and a centre tapped ground)...

Schematic attached, code to follow...


PCB has changed a little, here's the current version...


Just realised some of the caps in the schematic are 220uF... they need only be 100uF or even less...
Mike

[Koala]

Coil is about 8.5" and 29 turns of .71mm copper enamelled wire.

Just over 12" on a one pound coin. Not optimised for that coin so I would expect another inch or so would be possible at the sacrifice of other targets.

12V AA battery pack

In the photo you can see the Barclays fridge magnet that's not detected

Version 2 PCB without the switch and other FET taken off

~[ATTACH]35845[/ATTACH

I will try and get a better photo tomorrow

[Qiaozhi]

Good progress. Still don't see why some work and some don't. I take it my Earth field is working correctly with no modifications. Those advertising fidget magnets made out of magnetic paper have no affect on the threshold. Is this a valid test ??

It seems to depend on the Baracuda PCB version, and the battery pack voltage.
Which version do you have? What is the battery pack voltage? And what detection distance are you getting on a pound coin? Also, what are the details of your coil?