My new design - your opinion is needed :)

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Hi,

I am finishing my master degree work and I would like to share your opinion about my circuit design.
Any remarks are welcome! :)

Additionaly I have few quetions you to ask :

1) What values should be C1 and C4 from the first pdf ?

2) Also in the first pdf on the circuit which is responisble for power supply there are capacitors C10, C8, C11, C9, C7, C2. Of what values they should be.
I need 0,4 [A]of 12 [V] current so I suppose in the place where is 12[V] power supply I should have bigger caps ??
The same is with caps c13, C6, C5, C3 in second pdf but I don`t have there 12[V] power supply.

3) As you can see in the scecond pdf I have diode on pins PC4 and PC5 and my question is do it can affet ADC converter somehow ??

4) What about resets lines ? Do you think R - 4.7k is enough prottection for reset line or should I also give capacitor ?

5) Connecting Ftdi chip I was following instructions from this website:

http://www.sparkfun.com/commerce/present.php?p=BEE-8-EagleSchematic
Do you think in this design I can go without Ferrite bead inductor ??

Generally what do you think about my design ??
I have not done many of them on PCBs.
Mainly so far I made my projects on breadboards.
This time I have to do it on PCB and I will use it to support my master thesis.

Below are pdf documents with circuit designs !

symulator_schema.pdf is the first pdf
interpolator schema.pdf is the second pdf

Thanks in advance

Adam

Attachment(s): 

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10 uF and 100 nF should do for C1 and C4. C10 etc. should be according to the regulator data sheets.

Leon

Leon Heller G1HSM

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C23 is reversed: the open "line" is plus (old european symbol btw)
X6: 9 pole sub D but not for RS232 I guess
Pin 3 of LCD should be Contrast: connect to wiper of 10k pot, which is between +5V and Gnd. OK for most 44780-displays. Some require a negative voltage.
Analog ground should be connected to digital ground ..... somewhere

What is the secondary voltage of the transformer, and what power-rating is it ?

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tricia, and Ulyana. You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Thank you guys :)

Yeah one cap is reversed my inattention ;)
I don`t know exactly what did you mean by saying :

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X6: 9 pole sub D but not for RS232 I guess

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Pin 3 of LCD should be Contrast: connect to wiper of 10k pot, which is between +5V and Gnd. OK for most 44780-displays.

I don`t want to have regulated contrast. I just want it to be max ;) so that`s why it is tiedto the ground ;)

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Analog ground should be connected to digital ground ..... somewhere

Well I don`t think so Are you talking about mass from the ADC converter ??
When you connect analog ground with the digital ground analog ground will take half current from the digital ground which means you will have errors. Dont forget that the wire also has some resistance ;).

Thank you for replays but I thought more people would share their opinions ;)

Adam

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1. The 9-pole connector: if you use it for something else than RS232 you're fine.
2. LCD: if contrast is set too high, all you see is black boxes coming ;)
3. Whether you agree or not: you must connect digital ground to analog ground somewhere. Reason that Atmel brings them out on two separate pins, is to allow the PCB-designer to define where he/she wants to connect them.

How much thought have you given to the remaining questions yourself ?
What is the answer to my question ?

Nard

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tricia, and Ulyana. You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Sorry Nard !

I missed your sentence ;)

Transformer is 16 [V] and 1.07 A. I need to use such a big transformer because optoelectronic converter takes like 0.3 [A].

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LCD: if contrast is set too high, all you see is black boxes coming

Yes that`s tru I don`t have an idea how it is working now ;) :))))))))
Have to look at my breadboard ;)

Quote:
Whether you agree or not: you must connect digital ground to analog ground somewhere. Reason that Atmel brings them out on two separate pins, is to allow the PCB-designer to define where he/she wants to connect them.

Yes but what I meaned is that it is better to ground it near main ground. In this way you have more chances that there is no dropping voltage on wire from digital circuit.

What abou my other questions?
Well still thinking about capacitors etc. But I am close to the best solution. ;) Everything is working now but I want bring things up to scratch.

Adam

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Quote:

Quote:

Analog ground should be connected to digital ground ..... somewhere

Well I don`t think so Are you talking about mass from the ADC converter ??
When you connect analog ground with the digital ground analog ground will take half current from the digital ground which means you will have errors. Dont forget that the wire also has some resistance Wink.

Analog and digital ground MUST BE CONNECTED at ONE POINT. You will have almost no errors in ADC measurements if you follow "PCB design rules".
The Ground net should use a star connection scheme. Create a low-resistance AGND line on the PCB to the DGND to a center point. The current-carrying Ground lines should use other lines on the PCB.
This way you will have no error in the ADC as the AGND line carries very low current. From the star ground point (where all voltages are referenced from) the only error (offset) you may see is the resistance of the AGND line multiplied by the current from the AGND pins of the AVR.

For improving the measurements there are more possibilities in the AVR for switching off unnecessary parts during AD conversion. You can find them in the AVR datasheet at the Power Management and Sleep Modes.
There You will find the ADC noise reduction feature.

This way your error will not be noticable as the ADC has only 10bit resolution.

100 nF capacitors for ICs supply line you should use tantalum capacitors with X7R dielectric characteristic as close to the ICs as possible.

For the power supply part the main capacitors should be a larger value (10uF will be fine as suggested earlier) aluminum electrolytic parallelled with a lower value (100nF will be also fine) X7R tantalum.
You could connect a 0.1-2 Ohm resistor between the two capacitors.

Regards,

Peter

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Congrats on working towards your Master's Degree.

As others may be reviewing your design, it would be desirable to use "standard" or "recommended" design practices, not just "something that works".

The contrast setting on the LCDs is a user made adjustment to optimize the contrast for best viewing. The "recommended" design is typically a pot, (perhaps 10K), between V+, (5V), and either Gnd, or a negative voltage, depending on the particular LCD, as noted by Plons, above.

If the LCD manufacturer thought that 0 V, (Gnd), was the best, for all of the displays coming off their line, for all circuits, it would be internally connected to Gnd, and the pin and signal would not exist.

The optimal contrast voltage to that pin may not always be 0 V, (Gnd), and hence it is recommended to make it variable, and user adjustable. For some devices that may mean the control is a mini-pot, on the circuit board, set by the builder. For other designs it may be adjustable by the end user, (i.e. a front panel control).

The concept, however, is that tieing it directly to Gnd, without a pot, is an unreliable design that will give one a poorly visible, or completely non-readable display, at least sometimes.

If you are only building one device, and it works, you may chose not to change the design. However, you should understand that you took a short cut, and the possible consequences of your decision, particularly if you may be asked to "defend" your design with your thesis presentation.

JC

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Congratulations with the Master degree! But I am affraid you have still a long way to go.
I guess you can learn more from the guys here than you did in the last years alltogether. They are showing a lot of patience explaining to connect Agnd to Dgnd, and how to properly regulate the contrast LCD... Please listen to them!

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peter_smith wrote:
Analog and digital ground MUST BE CONNECTED at ONE POINT. You will have almost no errors in ADC measurements if you follow "PCB design rules".
The Ground net should use a star connection scheme. Create a low-resistance AGND line on the PCB to the DGND to a center point. The current-carrying Ground lines should use other lines on the PCB.
This way you will have no error in the ADC as the AGND line carries very low current. From the star ground point (where all voltages are referenced from) the only error (offset) you may see is the resistance of the AGND line multiplied by the current from the AGND pins of the AVR.

Exactly Peter that`s what I tried to say :]

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Congrats on working towards your Master's Degree.

Thank you

Quote:

If you are only building one device, and it works, you may chose not to change the design. However, you should understand that you took a short cut, and the possible consequences of your decision, particularly if you may be asked to "defend" your design with your thesis presentation.

Yes but the point is that my master degree is about something else. About special algorithms which are implemented into uC. These algorithms are responsible for increment in measurment of the shift of the optoelectronic converter.

So Viax I have to dissapoit you here in Poland you won`t get a master degree for lcd connection. :D
For me microcontrollers are great tools which I can use to defend my theorethical thesis in practical way.

and Yes I listen That`s why I posted this thread to listen what other people say about my design ;)

Take care you all and thanks for supporting me :)
I have already made change with LCD, capacitors etc.
I think there will be more changes in order to fit everything nicely into board :)

Adam

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An 8 bit dac made out of 1% Rs might only have 5 or 6 bit res... need .1% Rs I think. Why not just get a dual 8 bit spi dac??

Imagecraft compiler user

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Quote:
An 8 bit dac made out of 1% Rs might only have 5 or 6 bit res... need .1% Rs I think. Why not just get a dual 8 bit spi dac??

Good idea to use a separated DAC. If you want to keep it more simple you can use a Parallell input DAC as well. You will not have to deal with SPI if you do not usually use AVRs and you are not very familiar with them.

I understand you are concentrating on the algorythms in the MCU, and not the hardware. But I think you should try to make the hardware in a professional way as well so you can show your knowledge in a more detailed way, and you can also impress your teachers much more.

Even if you are not a hardware guy, it is a good idea to follow the tips are added here as those are proven in reality and are proven by time as well. Also you will learn new things and in your later designs (which will be probably much more complicated) you will face with much less problems.

Also congratulations on working towards your Master's Degree!

Regards,

Peter

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Why not just get a dual 8 bit spi dac??

Yeah it would be a better idea but in my city there are

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3 shops and actually they all have run out of dac. I have already ordered many things form internet shops so ordering another parts and pay for the shipment is to expensive. So I have decided to use these r2-r ladder.
It has another advantage that it is really simple and it is simple to explain how it works :)
Quote:

I think you should try to make the hardware in a professional way as well so you can show your knowledge in a more detailed way, and you can also impress your teachers much more.

Yes actually there are not many of us who decided to do a practical work. But as I am always dexterous in assembling and disassembling everything what is connected with electronic I have decided to do one practical ;)

Adam

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Yeah it would be a better idea but in my city there are
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3 shops and actually they all have run out of dac. I have already ordered many things form internet shops so ordering another parts and pay for the shipment is to expensive.

I don't know if you used to order things from Farnell, but it is also available in Poland. They have a very huge number of products and the shipping is only 5 Euro. If you order before 8 P.M. the package will be delivered the next day.

Peter