Is this a major advance in PI sensitivity ??

[straton]

May I ask, what are you talking about? An average/amateur PI machine would have over 10000X amplification to get descent results. The that1510 has been tested my me over 3 years ago and it has major flaws. You get a bit over average, sensitivity, but it's still far away from a good commercial PI detector.

[6666]

Thanks for the tips and tutorial Moodz
those adaptors would be handy

[simonbaker]

Unfortunately there is not much that is not surface mount ... actually I cant think of any that are not also very expensive.

The most cost effective chips like the Wolfson range offer 192K sampling ( and $5 price range ) and come in TSSOP. You can get TSSOP and other similiar adapters from here ....

http://www.futurlec.com/SMD_Adapters.shtml

This makes the use of surface mount very easy and very cheap.

Soldering is faster than soldering a DIP

1. Borrow the iron ( clothes not solder ) off your missus.
2. Buy an Infrared heat lamp at the local hardware store ( $10 )
3. Apply solder flux paste / liquid to the adapter board and "tin" the pads with a small amount of solder on the end of a soldering iron.
4. Apply some more flux and place the chip so it sits on top of the tinned pads ( the flux will act as a "glue" to hold the chip in place.
5. Put the iron on maximum heat and place the board on the iron ( using the iron as a heated platform or work area ).
6. The infrared lamp radiates the top of the board and is used to bring the final temp up to soldering temperature. The chip will "align" when the solder reflows and grabs the chip pins.
7. Once the iron is set up and using pretinned boards you can solder 20 chips in 5 minutes using this method.

The use of solder flux cannot be stressed enough ... you can buy 10 ml tubes of the stuff on ebay for about $5. Gunk it on so that the work surfaces are submerged in it when soldering. You will find that you will have trouble bridging even a 0.1 mm gap with solder when using good flux.

Of course you can also just solder by hand ...search utube for solder and TQFP etc and you will see lots of examples ... no fine soldering iron required ....I have used a quarter inch tip and 80 watts to solder SSOP and TQFP ( the secret is to use lots of flux , little solder and stroke outward along the line of the pins ... does not matter if the tip covers several pins at once. clean the tip often ).

Wash the boards afterward in a glass container using boiling water and a drop of detergent this will remove flux and finger contaminants. Put boards out to dry on paper towel whilst still hot.



moodz.

Those adapters definitely would be in order for my kind of prototyping. I'll keep that in mind. It's true most of the best new parts are SMT these days.

I still think we should pass a federal law requiring all parts to have non-SMT versions available ...

-SB

[hdphilip]

Can't agree more

seems that any chip worth designing with is surface mount.
although, moodz's fpga project may be a bit of a challenge with my current PCB process

Philip

all the space we save by usuing smd, we can replace with li-po's...

[moodz]

Thanks! Is this the best bang for the buck, or is there something cheaper that works in the 160 ksps range? Also important... not surface mount!

Regards,

-SB

Unfortunately there is not much that is not surface mount ... actually I cant think of any that are not also very expensive.

The most cost effective chips like the Wolfson range offer 192K sampling ( and $5 price range ) and come in TSSOP. You can get TSSOP and other similiar adapters from here ....

http://www.futurlec.com/SMD_Adapters.shtml

This makes the use of surface mount very easy and very cheap.

Soldering is faster than soldering a DIP

1. Borrow the iron ( clothes not solder ) off your missus.
2. Buy an Infrared heat lamp at the local hardware store ( $10 )
3. Apply solder flux paste / liquid to the adapter board and "tin" the pads with a small amount of solder on the end of a soldering iron.
4. Apply some more flux and place the chip so it sits on top of the tinned pads ( the flux will act as a "glue" to hold the chip in place.
5. Put the iron on maximum heat and place the board on the iron ( using the iron as a heated platform or work area ).
6. The infrared lamp radiates the top of the board and is used to bring the final temp up to soldering temperature. The chip will "align" when the solder reflows and grabs the chip pins.
7. Once the iron is set up and using pretinned boards you can solder 20 chips in 5 minutes using this method.

The use of solder flux cannot be stressed enough ... you can buy 10 ml tubes of the stuff on ebay for about $5. Gunk it on so that the work surfaces are submerged in it when soldering. You will find that you will have trouble bridging even a 0.1 mm gap with solder when using good flux.

Of course you can also just solder by hand ...search utube for solder and TQFP etc and you will see lots of examples ... no fine soldering iron required ....I have used a quarter inch tip and 80 watts to solder SSOP and TQFP ( the secret is to use lots of flux , little solder and stroke outward along the line of the pins ... does not matter if the tip covers several pins at once. clean the tip often ).

Wash the boards afterward in a glass container using boiling water and a drop of detergent this will remove flux and finger contaminants. Put boards out to dry on paper towel whilst still hot.



moodz.

[moodz]

ADS1675

this has recently dropped to $53.00 here in oz

Yeh ... kinda expensive ...especially if you make a soldering mistake

However it is good bang per buck on a samples per dollar basis for a 24 bit converter. 40000 / dollar which is comparable to your lower sample rate converters.

moodz.

[6666]

ADS1675

this has recently dropped to $53.00 here in oz

[simonbaker]

ADS1675 :-)

Thanks! Is this the best bang for the buck, or is there something cheaper that works in the 160 ksps range? Also important... not surface mount!

Regards,

-SB

[moodz]

I'll second that. Bookmarking. It should be added to our permanent "parts bucket" web page that doesn't exist.

However, I'd also like to find a faster ADC, with at least 160 Ksps and 24 bit.

Cheers,

-SB

ADS1675 :-)

[simonbaker]

Moodz, Nice find on the MCP3903. The pga, phase delay and 16bits make for an interesting mix. Ordered some today.

Thanks

I'll second that. Bookmarking. It should be added to our permanent "parts bucket" web page that doesn't exist.

However, I'd also like to find a faster ADC, with at least 160 Ksps and 24 bit.

Cheers,

-SB

[nick_f]

Driving the capacitors C6 +C7 with the TC4421, slows down the switch OFF speed considerably. This has a lot of influence on the Flyback and damping time.

Tinkerer

Hi Tinkerer,
I also didn't like the idea to use the same signal driving the coil mosfet and the converters for the power supply. It would be better to use two separate TC4421 or maybe to separate the outputs of the one used, one output for mosfet and one for DC-DC converters.
I am not sure if there will be any improvement in the real circuit, since I have not tried any of this.


PS - I should have read more, Moodz already explained the minimal effect of using the caps C6 and C7 on the same output of TC4421...

Regards,
Nicolae

[Altra]

Moodz, Nice find on the MCP3903. The pga, phase delay and 16bits make for an interesting mix. Ordered some today.

Thanks

[6666]

Can be ordered through RS components Sydney.
6-8 days wait , free postage in Oz

MCP3903-E/SS
Qty Unit Price
1 $4.12
5 $3.76

[moodz]

...and the WINNING ADC chip is .....

MCP3903 ( or MCP3901 if you are a real tight ***** )

This chip was made for metal detecting ( or should have been )

6 separate ( not muxed ) 24 bit ADCs with a programmable gain amp in front of each channel. Also a handy dandy phase shifter built in ... ( hmmmm )
Low power and LOW price ( mine were A$ 3.90 each )
... made by Microchip so they bolt straight onto the dspic chips. ( eat my shorts AtMega )

see full spec pdf here ...http://ww1.microchip.com/downloads/e...Doc/25048B.pdf

My initial testing shows that the spec is very conservative and the noise performance is much better than the quoted figures.

The UNIPI chip code is under test now.

Features
• Six Synchronous Sampling 16/24-bit Resolution
Delta-Sigma A/D Converters with Proprietary
Multi-Bit Architecture
• 91 dB SINAD, -100 dBc Total Harmonic Distortion
(THD) (up to 35th harmonic), 102 dB Spurious-free
Dynamic Range (SFDR) for Each Channel
• Programmable Data Rate up to 64 ksps
• Ultra Low-Power Shutdown Mode with <2 μA
• -115 dB Crosstalk Between any Two Channels
• Low Drift Internal Voltage Reference: 5 ppm/°C
• Differential Voltage Reference Input Pins
• High Gain PGA on Each Channel (up to 32 V/V)
• Phase Delay Compensation Between Each Pair
of Channels with 1 μs Time Resolution
• High-Speed Addressable 10 MHz SPI Interface
with Mode 0,0 and 1,1 Compatibility
• Independent Analog and Digital Power Supplies
4.5V - 5.5V AVDD, 2.7V - 3.6V DVDD
• Available in Small 28-lead SSOP Package
• Extended Temperature Range: -40°C to +125°C
Applications
• Energy Metering and Power Measurement
• Portable Instrumentation
• Medical and Power Monitoring
Description
The MCP3903 is a six-channel Analog Front End (AFE)
containing three pairs made out of two synchronous
sampling Delta-Sigma Analog-to-Digital Converters
(ADC) with PGA, a phase delay compensation block,
internal voltage reference, and high-speed 10 MHz SPI
compatible serial interface. The converters contain a
proprietary dithering algorithm for reduced idle tones
and improved THD.
The internal register map contains 24-bit wide ADC
data words, a modulator output register as well as six
24-bit writable control registers to program gain,
over-sampling ratio, phase, resolution, dithering,
shut-down, reset and several communication features.
The communication is largely simplified with various
Continuous Read modes that can be accessed by the
Direct Memory Access (DMA) of an MCU and with
separate Data Ready pins that can directly be
connected to the Interrupt Request (IRQ) input of an
MCU. The MCP3903 is capable of interfacing to a large
variety of voltage and current sensors including shunts,
current transformers, Rogowski coils, and Hall-effect
sensors.

[moodz]

I mostly agree with your design philosophy, but I'm going to insert a new third step:
Research whether the subsystem you need has already been developed and is available for use, perhaps in another field. Make an honest assessment of whether you think you capable of improving it, if not use it as is. In other words, don't waste time reinventing the wheel.

Other than that my only point was that your 5th step is going to frequently send you all the way back to your 3rd step. Time is by far the biggest investment in this sort of development. So if you can avoid some of these cycles by starting with suitable quality components then even if you do spend a little more than strictly necessary on the bits, your still be well ahead. If you achieve the performance your after and start thinking about production then you can start thinking about economizing on components.

THe WM8788 is indeed a surprisingly cheap performer. I'm a little suspicious of how the datasheet is written though. Nothing is specified at its full data rate or pre-low-pass-filter.

Oh and I said a better motorbike...a moped is never going to be better than an R1.

Touch`e I guess I would lump research and not reinventing the wheel under the design step but I guess it is good to be explicit about it.
Recently I came across a power switching device that switches 8 amps, breaks down at 1700 volts and only has 20 pF output capacitance. So I bought 5 of them ( $20 a pop ) however there appears to be only one manufacturer and the application field in high efficiency solar regulators is changing so fast that I can just see these devices not being available in a couple of years.
Will I play with it ... yes .... Would I recommend it for a new design .... no ... for the reasons above.

On motorcycles ... We would expect an R1 to perform better than a moped. The real engineering challenge is to surprise everyone by designing a moped that out performs an R1 not the other way round.