Hi, how can i perform calculations to complete this DAC table ?

[nyame]

Hi, how can i perform calculations to complete this DAC table ?

[ataradov]

I appears that you want us to do your homework. That's called cheating.

[ogden]

Perhaps you can start with this:

https://www.electronics-tutorials.ws/resistor/res_4.html

[bson]

Also, the summing amplifier:

https://www.electronics-tutorials.ws/opamp/opamp_4.html

[nyame]

Hi, thanks for the reply,

but looking at the circuit i got only 4 bits, and i have been ask to complete the table with 8 coulomb, that is were i got some issues so please i need details calculations

[Rerouter]

I should point out the pattern by the first 3 examples,

Start by calculating what the parrellel resistance of each step is,

1/resistance=1/R1 + 1/R2 +.. etc

If you really dont want to try and calculate it, Fire up something like falstads circuit simulator

[nyame]

thanks for the reply, i know how to calculate the bits individually, the issue is i got 4 bits with a table of 8 coulombs how do i achieve results for all the 8 coulombs ?

[Rerouter]

You have 4 bits, of which your example only uses 3, 2³ = 8

When a bit is 1, It closes a switch for the given resistor on the board,

The 8 entries on the "Vout" column are completed by calculating based on the resistors connected,

As for the math, read up on the subject here, https://www.electronics-tutorials.ws/opamp/opamp_4.html

[Mechatrommer]

the attached zip file contains copyrighted xls file for 16 coulombs data. by downloading it you are agree to pay me $10 through paypal... 

[nyame]

Hi, thanks for the Aid.

but the solution you presented will only help someone with a good inside of electronics.
am a beginner so i will appreciate if you can perform the calculation in a more basic manner.

thanks

[rstofer]

You're not going anywhere if you don't know Ohm's Law and to be truly capable of figuring out what is happening, you need to understand Kirchhoff's Current Law.

In particular, you need to understand that the voltage at the - input is exactly the same as at the + input.  Op amps work to force that to occur.  As a result, the voltage at the - input is exactly zero.

Therefore, every bit of current that comes in through the input resistors flows out through the feedback resistor and there are some interesting mathematical properties that come about because of this.  So, this current (per path) is simply the voltage divided by the resistance.  All of those currents add and cause a drop across the feedback resistor.  Given that you can calculate the drop across the feedback resistor and the - input end is 0V, you can calculate exactly the output voltage of the op amp.

https://www.electronics-tutorials.ws/opamp/opamp_4.html

w2aew's video on summing op amp circuits:


More basic is his earlier video


I don't know what class you are taking but you need to gather up some background information before you will truly understand what is going on with this circuit.

I am not going to write the KCL equations, the videos will help with that.

[rstofer]

Hint:  Each resistor's current contribution to the - input terminal will be 9V / <resistor value> because one end of each resistor (the - input) is at ground.  This is true because the + input is at ground and the op amp works properly.

9V / 5k contributes 1.8 mA
9V / 10k contributes 0.9 mA
9V / 20k contributes 0.45 mA
9V / 40k contributes 0.225 mA

Notice I am dealing with currents.  Kirchhoff's Current Law.  The sum of the currents entering and leaving a node (at the - input) are exactly 0.  One other rule:  There is no current actually entering the op amp through either input.  So, all of the resistor current sums up at the - input and leaves through the feedback resistor.  None enters the op amp.

Note also how Ohm's Law is used to get the current through each resistor.

Let's see what happens when all switches are closed and all resistors are delivering current.

I= 1.8 + 0.9 + 0.45 + 0.225 mA or 3.375 mA

Now, the output voltage is simply the current (I) * feedback resistor or 0.003375*450 = 1.5 V and it's negative so -1.5V, the same answer Mechatrommer got.  Two different approaches to the same answer - I like it!

Now take your table, figure out which switches are closed and add up the appropriate currents from above.  Multiply the total current by the 450 ohm resistor, assign a - sign, and you are done.

Watch the videos!  w2aew does a magnificent job of explaining how this stuff works.

[rstofer]

A nice animation of op amps

[Simon]

I am sorry but this is not how you pass tests and get qualifications. OK you may end up passing and getting the qualification but will be shit at your job if you ever get a job. It's not that asking for help is bad. I also am studying and have had a lot of help on this forum. But I post here as a last resort and having done my best. I also don't expect to be just handed a solution but explain what i know so far and where I am stuck and ask for help in understanding not in being handed a solution to copy.

[nyame]

Thanks for the reply, the most important aspect is not getting the answer rather understanding the way it was solved including the formula, once I get the solving technics then am ok, so I don't see were the aspect of writing and copying is coming from. Mines are different we can't think the same, however Opion are meant to be expressed, but think before you judge. Once more thanks

[Simon]

You are asking for solutions to relatively simple problems. What materials are you studying? This problem is simply an opamp summing amplifier with a different gain on each input. Once you know the gain of each input simply add the input voltages multiplied by the gains.