Electronics > Beginners
DAC circuit
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Wimberleytech:

--- Quote from: nForce on January 26, 2019, 08:10:58 pm ---Yes, I understand you.

I am just using the knowledge from known values:
First-term the numerator has delta which is 3.3 V so the same reason for the motor the numerator would have 3000 which is delta. Delta is the difference between min and max.

--- End quote ---
No, the first expression converts bits to volts.  The second expression converts volts to volts.  The third expression converts volts to RPM. 

In term of units:
(Volts/bit) (Volts/Volts) (RPM/Volts) = RPM/bit  <--K

If your DAC input changed from 2000 to 2001, a delta of 1 bit, then using the equation, RPM would change by a delta of:

1 * (3.3/4095) * (10/1.65) * (1500/10) = 0.732 RPM

nForce:
OK, now I understand in terms of units.

Can you just say why is then 1500 rpm? Or maybe another person can write it.

Let's be consistent:

The first term: delta = 3.3 V - 0 V = 3.3 V
Last term: delta = 1500 rpm - -1500rpm = 3000 rpm.
Wimberleytech:

--- Quote from: nForce on January 26, 2019, 10:14:49 pm ---OK, now I understand in terms of units.

Can you just say why is then 1500 rpm? Or maybe another person can write it.

Let's be consistent:

The first term: delta = 3.3 V - 0 V = 3.3 V
Last term: delta = 1500 rpm - -1500rpm = 3000 rpm.

--- End quote ---
No, you misunderstand "delta"
In the first term 3.3/4095 just the transfer function from the D input to the output of the first amplifier.

As far as 1500rpm.  That is just the designer's choice based on motor used.  No magic.
nForce:
Why the first term the range 0-3.3 V is not delta? It seems to me that all the data on the schematic is consistent.

Omg, this is going to take forever.  :(
Wimberleytech:

--- Quote from: nForce on January 26, 2019, 10:42:39 pm ---Why the first term the range 0-3.3 V is not delta? It seems to me that all the data on the schematic is consistent.

Omg, this is going to take forever.  :(

--- End quote ---
3.3V - 0V is indeed a "delta"

BUT, that is not the first term.  The first term is a transfer function as I said.

How long this takes depends on you.  I understand the circuit and the equations.

You should install LTSPice if you have not already done so.  I will upload the LTSPice file and you can play with it.  Maybe it will help you get a feel for what is going on.
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