Sine wave power inverter

[sougata]

Hi Dayama,

What you are proposing is a dual conversion design. When you have a battery bank of greater voltage it makes sense other wise for a 12/24 volt system consider this.

1. The Primary current will in the order of 50 AMPs so it is necessary to use copper bands for the primary windings.

2. Frequency has to be kept high (ferrites) consider the switching losses of the primary MOSFETs

3. You have two different switching stage so a single PIC may complicate your programming issues.Of course you can use a ready made SMPS controller like the SG3525 but then this forum may not be the right place to discuss.

4. Microchip has a very good appnote on such type of design.

If you are using PBP then this forum will help you out in solving problems.

One of my laboratory power supplies runs on a PIC for a Buck regulator.

We get only a limited supply (not all models) of cosmo ferrites so it is beyond my scope of experiment. However I would definately like to meet you while I am in Mumbai.Send me a private email if you are interested.

Regards

Sougata

[psdayama]

Dear Saugata,
please read my comments pointwise:

Hi Dayama,

What you are proposing is a dual conversion design. When you have a battery bank of greater voltage it makes sense other wise for a 12/24 volt system consider this.
1. The Primary current will in the order of 50 AMPs so it is necessary to use copper bands for the primary windings.

When one is making Inverter/UPS then the transformer and MOSFETS
have to handle this currents and I have seen atleast 3in parallel to do this.
I think It is OK for 500VA and for 1KVA one has to use 24V battery for same
purpose. Higher rated systems are using batteries 48V or even 110V!!!

2. Frequency has to be kept high (ferrites) consider the switching losses of the primary MOSFETs.

Frequency has been optimised to 40-60KHz for considering this aspect.
I would like to use more than 100Khz if possible but then MOSFETs would be
beyond reach.

3. You have two different switching stage so a single PIC may complicate your programming issues.Of course you can use a ready made SMPS controller like the SG3525 but then this forum may not be the right place to discuss.

My design has 3 switching stages. a)First for conversion to 12V from 230V(SMPS), second a simple Inverter to convert 12Vdc to 300V dc dual supply and lastly the Sinewave converter with half bridge for direct output.
SMPS is based on SG3525 and dc to dc also same but they can have analog
control inputs with additional PWM from Microchip instead of DAC.The last converter is entirely based on Microchip and same chip can used for other indication or control functions. One has to consider the entire system development and how to make optimum use of available resources. It is just
not possible to use one PIC for all functions reqd.

4. Microchip has a very good appnote on such type of design.

Please do send link for that design.

5.If you are using PBP then this forum will help you out in solving problems.

Im not aware of PBP. I am doing programming in Assembly and use a
program to convert it in code.

6.One of my laboratory power supplies runs on a PIC for a Buck regulator.

Im very interested know about it.

7.We get only a limited supply (not all models) of cosmo ferrites so it is beyond my scope of experiment. However I would definately like to meet you while I am in Mumbai.Send me a private email if you are interested.

Regards

Sougata

Please visit cosmo ferrite website. They have dealers all over India and
Kolkata must be having some. If U want some hard to get size then I can
help. But for regular supplies the company will gleadly contact U.
I think I have missed Ur reply due to incorrect setting of intimation. Im
sending U private email for details.
Thanks,
psdayama

[barkerben]

I made a 24v, 250W Quasi sine wave inverter using a basic PIC (can't remember the exact details) a couple of years back.

It used quasi sine rather than full sine - in other words, a square wave with dead time. Having said that, regulation was less than 10% at full load, and efficiency was over 95%. Quite good fun really...

[psdayama]

I made a 24v, 250W Quasi sine wave inverter using a basic PIC (can't remember the exact details) a couple of years back.

It used quasi sine rather than full sine - in other words, a square wave with dead time. Having said that, regulation was less than 10% at full load, and efficiency was over 95%. Quite good fun really...

Quasi SineWave shouldn't require PIC !
Also regulation seems to poor as even 1% easily achievable. May be U have
some special functions so U are welcome to elaborate.
psdayama

[barkerben]

I think we used a PIC for two rasons. Firstly, we wanted the option of going to full sine wave. Secondly, we could eliminate regulation by dynamically changing the deadtime in the quasis sine wave. The 10% (I think it was 10% - lng time ago now) was without any feedback, when running at full load (250W). The PIC was also useful at startup.

Ben

[psdayama]

Hi barkerben !
thanks. It was just curiosity as just few months ago Electronics For You (EFY)
India magazine has published simple inverter with just few ICs and Mosfets.
Of course there are some commercially available inverter cards (Digital Inverter)
with PICs costing no more than Rs.500/- with Quasi sinewave output and frills
of DSP. These are good for PCs and lighting but give lots of problem with fans & motors. They also give regulation of better than 1% in inverter mode and +/-10% in mains mode.
psdayama

[barkerben]

Yep - our circuit may not have been all that good after all, but it was good fun to make! We were building from scratch as much as possible - winding our own transformers, etc. There were a few of us doing it at once. One group had a novel way of stopping their mosfets from frying - a constant stream of freeze spray! Not exactly very practical, but certainly impressive :-)

One group tried a resonant inverter, but got bogged down with the problem of sensing the load parameters to match the resonance...

[barkerben]

Oh yes, that was it... I remember now.

We had 24v in, chopped using a full bridge to 20Khz AC, fed into a transformer, then rectified to high voltage DC using a diode ring. The ide of high frewuency was to reduce transofrmer size and losses. The high voltage DC was then chopped usign a second H bridge to a quasi sine output.

The trigger signals for both bridges were generated by the PIC. We wanted to replace the quasi sine bridge trigge with full sine, but never got around to it :-(

[psdayama]

Oh yes, that was it... I remember now.

We had 24v in, chopped using a full bridge to 20Khz AC, fed into a transformer, then rectified to high voltage DC using a diode ring. The ide of high frewuency was to reduce transofrmer size and losses. The high voltage DC was then chopped usign a second H bridge to a quasi sine output.

The trigger signals for both bridges were generated by the PIC. We wanted to replace the quasi sine bridge trigge with full sine, but never got around to it :-(

That was good!!! U should have made the output of hi freq. transformer centre tapped and used bridge to get dual supply i.e. +/- side. This requires
only half bridge ckt and only 2nos of Hi voltage Mosfets and get good sine wave
from it.(U require small inductor/capacitor filter for non inductive loads.) Again U can prevent the Mosfets from frying with including some current limiter in HT side rectified high voltage rather than spraying freezant.

[robinjacob]

Hi Sougata,
Have you finally designed the sine wave inverter? I am really interested to see the design. If you can please send me a schematic.

Thanks and Regards
Robin Jacob.

[psdayama]

Hello!
just scroll down and U will find the schematic in jpg format.
I don't know if Saugata will give the code.
Some part he has already explained.

[sougata]

Hi there,

I did finish the project and managed low harmonic content and descent crest factor but need to improve on the distortion issues on mixed inductive loads.Please note that it is a commercial project and I just cannot share it on this forum. However I would certainly like to answer specific queries.

Off the track I would like to express my gratitude to PSDayama whome I met personally on my trip for the Microchip Master's Conference. A warm welcome and great hospitality moved me. I thank this forum too.

Regards

Sougata

[psdayama]

Hi Everybody,
I met this nice chap SAUGATA thru this forum and very happy to
interact on subject which Im trying to learn from scratch.Of course
I am little old (>55years) but one is student all his life!
I want to thank the forum for getting to know many young people
and their expertise and exploits ;-)
Lets hope everybody gets on ahead with the subject matter.
Regards,
psdayama

[psdayama]

Following link gives description various design slides available:
http://ece-www.colorado.edu/~pwrelec.../slidedir.html
Check them for transformer & Inductor.
psdayama

[robinjacob]

Hi,
Atleast somebody give me a schematic of the inverter with uC. I would like to know about the snubber circuit and the ouput filter circuit. Could somebody help me out.

[dknagare]

Dear Saugata,
please read my comments pointwise:




When one is making Inverter/UPS then the transformer and MOSFETS
have to handle this currents and I have seen atleast 3in parallel to do this.
I think It is OK for 500VA and for 1KVA one has to use 24V battery for same
purpose. Higher rated systems are using batteries 48V or even 110V!!!


Frequency has been optimised to 40-60KHz for considering this aspect.
I would like to use more than 100Khz if possible but then MOSFETs would be
beyond reach.


My design has 3 switching stages. a)First for conversion to 12V from 230V(SMPS), second a simple Inverter to convert 12Vdc to 300V dc dual supply and lastly the Sinewave converter with half bridge for direct output.
SMPS is based on SG3525 and dc to dc also same but they can have analog
control inputs with additional PWM from Microchip instead of DAC.The last converter is entirely based on Microchip and same chip can used for other indication or control functions. One has to consider the entire system development and how to make optimum use of available resources. It is just
not possible to use one PIC for all functions reqd.



Please do send link for that design.



Im not aware of PBP. I am doing programming in Assembly and use a
program to convert it in code.


Im very interested know about it.


Please visit cosmo ferrite website. They have dealers all over India and
Kolkata must be having some. If U want some hard to get size then I can
help. But for regular supplies the company will gleadly contact U.
I think I have missed Ur reply due to incorrect setting of intimation. Im
sending U private email for details.
Thanks,
psdayama

I have tried 3 to 4 designs of this type of technology. About 5 years ago i used SG3525 @ 50KHz for battery boost 12VDC to 320VDC and then chopped with squarewave 50 Hz using again SG3525. I have used full bridge for DC to AC conversion. The result is very satisfactorily over 5 Years of cont. use now I am trying to make it sinewave within a month or so it will be ready.

[sougata]

Hi,

I originally posted this thread and I would like to know the details what you are actually trying to do.

[dknagare]

Hi,

I have already tried transformerless( only small ferrite core of EE65X13) design upto 1000W but output was squarewave. Now I will use SPWM signal to convert DC to AC. In this type it easily possible to make 3Phase output without much circuit.

My main aim is to make sinewave inverter without using bulky iron core. I will upload some details very soon.

[psdayama]

Hi,

I have already tried transformerless( only small ferrite core of EE65X13) design upto 1000W but output was squarewave. Now I will use SPWM signal to convert DC to AC. In this type it easily possible to make 3Phase output without much circuit.

My main aim is to make sinewave inverter without using bulky iron core. I will upload some details very soon.

Thanks a lot for information. For long time nobody posted and Saugata is
busy with his own projects. I also came across one commercial model which
didn't have any bulky transformer but only small ferrite ones like in smps.
I think I sent my block diagram to Saugata. I have changed OS in my PC and
it is difficult to locate it but I will get and put it here.
My idea was to have inverter with output switched by fast relay for crossover. Also if we don't use relay and instead use directly take out output
from inverter and meanwhile have heavyduty charger, we get cheapest
online UPS. For this there can't be output transformer and so output has to be HalfBridge type with centre tapped power supply. To get this advantage
we have to put premium on the Mosfet/IGBT voltage.(Require withstand voltage atleast 800 to 1000V) but that is better than some 10Kg transformer
for 1000W type and also price about 1000-1200/-.
I am also having one inverter with high frequency chopping but its output is
50Hz and so transfomer is very bulky.
Now I pray that sooner or later Saugata will tell us about new design !!!

[dknagare]

Hi,

Can anybody provide me schematic diagram of output stage of HalfBridge as could not found application for dual voltage tapping +/- since the gate voltage should not exceed to say 20 V w.r.t. source of lower side Mosfet/IGBT. This can be achieved by using Bridge driver IC, but I could not find any practical application for it, however a separate bridge driver like TLP250 can be used but practically I have not yet used. Is anybody enlight/share on this with their experience.

[psdayama]

Hello!
I already informed U in pvt mail that U have to use either Pulse txrs or
opto isolators for driving. Bridge driver ICs don't work more than 100volts.
All U have to do is put the txrs/optos in output of Ur circuit or use simple
bridgedriving ICs and txrs. In case of Opto's U have to steal driving current
with high resistors and zeners and use 1more transistor/gate to make fail-safe. Means when signal the FET remains off. I think that in this respect
the pulse transformers are ideal solution and cost no more than Rs.12-15 each. U can also borrow some technic and keep the gate reverse biased
during off period.
Many circuits are available on Fairchild's website as they have most the
driving ICs and POWER mosfets.

[sougata]

Hi Dayama,

I am sorry I couldn't be in touch as I am under terrible pressure handling some railway projects. I am a one-man army as you know.

Back to the topic:

1. Any improvement or innovative idea is welcome.

2. My sinewave inverter is running successfully (24VDC-240AC~50Hz) but cannot share the schematic and code as I am commercially bound.

3. Should there be any PIC related problem I will surely try to help within my knowledge boundaries.

4. I have already done a PIC16F676 based squarewave UPS design (inspired by a forum member) and currently testing it.

5. I am working with PIC16F73 to port my design of sinewave inverter into a small offline UPS.

6. Double conversion is okay but generally more complicated and may be expensive in terms of ROI. What I have found is that boosting the voltage from 24VDC to 384VDC (to create a 240V AC) is less efficient. May be due to my limited knowledge on designing sm transformer. A 48V DC based boost converter gives better result.

7. I would be working on a different technology from June onwards that promises to deliver sinewave output using a single stage and ferrite transformer. I don't know whether I would be successful there as it is my own project and have limited funding. If I can spent time and get some fruitful results I will post them here.

8. Regarding MOSFET drive what I have realised is that a soft turn-on reduces harmonics and a fast turn-off is necessary to cope for switching losses. Also ringing should be well controlled otherwise bursts for no apparent reason. And never use the Microchip drivers. They are real crap. I followed every guideline and got terrible results. IR, Toshiba great. In fact I asked in the Master's conference that why Microchip is using IR gate drivers on their dSPIC motor control board when they have there own product line.

[psdayama]

Dear Saugata,
thanks for writing. It has been long time to see U or some posts.
We all understand that U are helping the forum but U have Ur own army
to care and feed :-)

Now about Ur points:
1.& 2. We would never ask U to divulge Ur commercial secrets for FREE!
3. I have yet to commence the exploration of PIC. As I told U I am
doing all prokects in other world but ultimately it is a 8bit and uC thing.
So just nomeclature changes but basic things are same. I find that ATMEL
has also put up ARM type which are just as good as PIC and I don't have to change the assembly language. But sure will ask about PIC in few days after
finishing old projects.
4. I am also thinking about same PIC16F73 but I think other 676 has more PWM outputs which can of great help.
6.Ferrite transformer design is no big deal if U have designed iron core one.
There are many websites which have actual examples.Also if U can convert
48V to 300+ volts then 12-24 V to same is also not differrent. Just have some
more conductors and that helps for high frequency. For example I had make
primaries of 11SWG but instead I used 2 conductors in parallel of 14SWG.Nice thing about ferrites is that U need only few turns as turns/volt are as much as
40times less.
7. am hoping to know what 'new technology" U are talking about. Surely it will be very interesting for the thread of "sine wave inverter"
8. U have correctly stated the position of fast and slow turn on. Everybody
has to make decision about switching losses and surge supression and cost off higher voltage device. As far as Bridge drivers i hate those and I rely solely
on pulse transformers or opto couplers.
regards,
psdayama

[batee]

Hi,

Can anybody provide me schematic diagram of output stage of HalfBridge as could not found application for dual voltage tapping +/- since the gate voltage should not exceed to say 20 V w.r.t. source of lower side Mosfet/IGBT. This can be achieved by using Bridge driver IC, but I could not find any practical application for it, however a separate bridge driver like TLP250 can be used but practically I have not yet used. Is anybody enlight/share on this with their experience.

IR2184 is a high side AND low side driver. It generates the extra 10-15V needed above the bridge supply voltage to turn on the top FET, and gets you dead time protection and logic-level inputs, too. It's good for up to 600V, unlike every other FET bridge driver I saw. Two are needed for full bridge operation. If you need programmable deadtime, use the 21844.

Half-bridge schematic is included in the datasheet.

http://www.irf.com/product-info/data...ata/ir2184.pdf

Good luck,

Bryan A. Thompson
[email protected]

[psdayama]

IR2184 is a high side AND low side driver. It generates the extra 10-15V needed above the bridge supply voltage to turn on the top FET, and gets you dead time protection and logic-level inputs, too. It's good for up to 600V, unlike every other FET bridge driver I saw. Two are needed for full bridge operation. If you need programmable deadtime, use the 21844.

Half-bridge schematic is included in the datasheet.

http://www.irf.com/product-info/data...ata/ir2184.pdf

Good luck,

Bryan A. Thompson
[email protected]

Hi,
thanks but this driver may not be useful as the half bridge ckt we are discussing. I went thru the datasheet and driver ICs Vcc is referenced to
lower mosfet. However in our case the lower mosfet source is - 350 volts so there may be problem. D.K. Nagare has used pulse transformers which are
proper and no headache for driver configuration. He had problem due to voltage rating of Mosfet (600V type used in 700volt ckt). I hope he has found
the circuit working with say atleast 800V rated mosfets. I have suggested a
high value resistor network so that at output of bridge each mosfet has nominally 350V to withstand.
Hope to hear from U again,
psdayama

[batee]

A capacitor pump of +12V referenced to the center of the bridge allows the top FET to turn on. I tried it at +170V top, 0V bottom and it works great, but agree the 700V would exceed its ratings.

Why generate a split source to power the inverter? I've not seen that done before. It seems like the cost of the copper and the extra DC link capacitor outweighs the cost of a couple of extra transistors.

If you're custom-winding a transformer to achieve this, can't you just add a tap at +/- 350V and another at +/- 360V to allow a simple level shifter transistor to turn on top FET?

[batee]

Has anyone looked into using a DDS IC like the AD9833 for an inverter application? What were the results? How did you achieve PWM from the analog output?

Bryan A. Thompson
[email protected]

[psdayama]

A capacitor pump of +12V referenced to the center of the bridge allows the top FET to turn on. I tried it at +170V top, 0V bottom and it works great, but agree the 700V would exceed its ratings.

Why generate a split source to power the inverter? I've not seen that done before. It seems like the cost of the copper and the extra DC link capacitor outweighs the cost of a couple of extra transistors.

If you're custom-winding a transformer to achieve this, can't you just add a tap at +/- 350V and another at +/- 360V to allow a simple level shifter transistor to turn on top FET?

Problem is U haven't caught the thread! We are discussing eliminating
bulky 50Hz transformer for Inverter/UPS. Now there are upteen circuits with psudo sinewave output which are not upto mark in many situations like
running fans. What I have been proposing that instead of using PWM for
sinewave generation from battery there should be high frequency DC to DC
converter and the PWM drive the Half Bridge ckt. Now the load can be connected to output of inverter or normal mains supply just by switching
with relay and referenced to Neutral. Also if U don't want to switch then
U just arrange for proper battery charger and keep inverter always on making
online UPS.
I have found that the transformer costs whopping Rs.1200/- and weighs
more than 7kgs for 500VA output. On the other hand whole inverter costs as
much that amount as we use Ferrite txr of small size operating at 40KHz.
Instead of costly driver ICs one should use Pulse transformer as they cost
just Rs.12 and have 2 windings also. I just checked cost of 800V mosfet which is 6-7 times costly than 600V type 6N60. So what I think that in this
case 2 Mosfets in serries in one leg of HalfBridge would work well with pulse
transformer having 2 secondary windings.

[psdayama]

Has anyone looked into using a DDS IC like the AD9833 for an inverter application? What were the results? How did you achieve PWM from the analog output?

Bryan A. Thompson
[email protected]

I haven't seen the AD9833 datasheet. In analog it is very simple to make
PWM. What U need is to make a reference sinewave oscillator. This U can find
from Opamps Application note of National Semiconductors. Oscillator uses
weign bridge and JFET to stabilise amplitude. Then U need a trinagular wave
of " carrier " frequency i.e. at which frequency U want PWM. U feed the
triangualar wave and sinewave to good comparator and Uget the PWM in output. If U want -ve side PWM also then U use one inverter for sinewave
and feed that to another comparator. And U get the -ve half signal for pwm.
There is interesting article about this on
url:http://www.drbrushless.com/

[batee]

Yes, I understand the ironless / transformerless concept. I also plan to use no transformers (step-up or step-down) or inductors in my design.

An advantage of DDS is that it is programmed via SPI, so a jumper change or RS232 command could make changes to waveform shape and frequency.

Pulse transformers and driver ICs appear to cost about the same here in Midwest US. I chose the driver ICs because they could be driven with logic level inputs regardless of the FET design.

It looks like more research money is going into 250V and 600V FETs and IGBTs than into any other voltage ratings, so that's where I have chosen to focus my designs.

Do you anticipate problems with running a system like this continuously (for months or years at a time)? Even if the FETs were well heatsinked and stay cool, I would anticipate continuous operation would degrade their lifetime.

Good luck guys.

Bryan

[psdayama]

Hi Everybody!
it seems that nobody is interested in this topic now.
I have found one interesting paper and hope everyone will have a look:

http://eprints.iisc.ernet.in/archive...ass_Of_PWM.pdf

In the 4th example circuit is what exactly I have been searching.
Also don't know where is D.K.nagare now. He said he has already made
prototypes and was doing field trials. Now he is vanished from Forum and
also from Yahoo.
Hope to hear from U soon.

[Navneet Vinaik]

Hi Everyone,

I have just started work on sinewave inverter using Metal transformer, using PIC microcontroller.
Can anyone provide me some tips.

[sayzer]

Navneet,

That is something that a lot of people are asking for.

If you find code examples pls remember to come back here and post.

--------------------------------

[mat janssen]

I made for an old friend a chip where he could select one of 16 sinewave frequencies to open a relay in a repeater (for transmitting)
Here is a part of the programm only one frequency (50Hz) is there now.
the rest is not important.
It gives the 50 Hz in 200 parts of pwm.
When putting a lowpass filter after the output. The sinewave is back.
Regards,
Mat

[psdayama]

Hi Everyone,

I have just started work on sinewave inverter using Metal transformer, using PIC microcontroller.
Can anyone provide me some tips.

Hi Navneet,
it seems that U are trying to reinvent wheel!
Please go thru the whole thread. In last post I mentioned one article
which is evaluation of PWM sinewave inverter. Also there has been discussion
on disadvantages of metal txr. If U can design proper program for sinewave
PWM then U can utilise ferrite txrs with switching frequency 25KHz and above.
The cost & weight of metal txr is major problem.
Rest wish U best of luck!

[Navneet Vinaik]

Thanks Psdayama, Mat and Sayzer.

I have downloaded the code and paper.
Can anyone guide me hw to calculate the pulse width's effectively?

[pramodsinha]

hi, everybody!
In the market lots of sine wave inverter available in pic 16f72 they are using software pwm not hardware pwm in the entire forum no body has discuss about software pwm , as 16f72 is very cheap and easily available.
I think we should explore about generating software pwm to create sine wave in a bridge configuration, I am trying to develope it and hope it will be successful in this month after finishing i will be able to put some light on it.
thanks

[sougata]

Hi,

My original design was based on a 18F452. Using both of the hardware PWMs and a sine weighted lookup table to modulate the PWMs at regular intervals. The interrupt routine also triggers an ADC to correct distortion on the output. So the ADC was sampled after every PWM steps. I found that the internal ADC was not giving me good results so used an external one. Now I realize that I actually complicated my design.



After the Master's Conference in Gurgaon India me and Pramod would be jointly working on a software based PWM sine wave UPS/Inverter this month. It is again a commercial project but we can sure shed some light and guide people by at least suggesting a way. A normal home UPS/Inverter does not need (at least here) a distortion free clean Sinewave. So we are restricting ourselves to the following criteria.

1. Low Cost
2. Low component count
3. Decent sinewave generation with only average variation for voltage regulation and no THD management.

Hope we successfully complete the same. We will get back here, since this is the place where we met.

[psdayama]

Dear Sougata,
Im very glad to see Ur post after long time. I wish U all the best for
seminar and subsequent planned development.
I too agree with Ur aims on this project. Please add few more:
a. The THD required is just around 10% and not 2-3% as claimed by
commercial units.
b. Voltage regulation of +/- 10% is also good which is same better than
what we get from regular utility cos.
c. It will be useless to get separate 2 HWPWM outputs as only one required.
All U have to do is get 4 steering outputs. 2 are used for alternate pulses
for PWM and 2 for half-cycles. If U use little hardware then (U have to use
it for deadtime) then 2pins can be freed and U need only 2 pins for halfcycles.
This way lot of real time saved and U can have more processing time for
interrupts.

Few posts ago somebody has posted the table for sinewave. I am surprised
that most people make table for 200 steps. I think that table should be of
1024 steps.One only has to generate 256 values for 0 to 90 degrees and mirror them for 90 to 180 degrees
to complete first half cycle and mirror entire thing for other half cycle.
This will give freq of 50*1024= 51200 Hz and carrier freq. half of that is
near to 25Khz for optimum use of Ferrite Txr instead of metal txr.
If internal ADC of 16f72 cant handle this then external one should be used
which can be as fast as 200Ksamples MCP3202 but this may increase cost by abt Rs.100/-
Dear PRAMOD, very glad to hear from U after long time.
I am still trying to find out if Hardware type card can be made within Rs.500/-
and hope to post same if successful.
regards,
psdayama

[MKA341]

hi

can you tell me about pic basic?

Manish