Hi all, me again.
I've learned a lot since I posted THIS thread earlier this month - most importantly, that every part of a digitial circuit needs to be carefully considered and engineered.
I focused on the LM393 comparator.
After searching 20-30 sights on the web, I found that there is a formal way to approach the construction of a LM393 circuit.
So I thought I would present what I did here, get some comments and ask a couple of questions.
Assumptions:
1. Vcc = 5V Vdd = 0V
2. Input voltage from 555 is 0-5 V
3. Arbitrary low and high thressholds of 1V and 3V
Then using R1/R2 = (Vth-Vtl)/(Vcc-Vdd) = 2/5 = 0.4
I arbitrarily chose two resistors that met the 0.4 ratio - 1,000 and 2,700 ohms
Then using Vref = Vth*R2 + Vtl*R1 / (R1+R2) = 3*2700 + 1*1000 / 3700 = 2.5V
Then calculating a voltage divider to generate the 2.5V reference voltage on "-" (easiest part, 10K each)
So here's the circuit, and when I breadboarded it, it seems to work fine.
Questions:
1. Is this the way you do it?
2. Are there any subtlties that I have missed?
3. How do you select the feed back resistor?
__I see many 1meg feedback resistors in circuits, but I don't know why. Mine's only 2.7k
__Any insight there?
Again, I thank you in advance.
I've learned a lot since I posted THIS thread earlier this month - most importantly, that every part of a digitial circuit needs to be carefully considered and engineered.
I focused on the LM393 comparator.
After searching 20-30 sights on the web, I found that there is a formal way to approach the construction of a LM393 circuit.
So I thought I would present what I did here, get some comments and ask a couple of questions.
Assumptions:
1. Vcc = 5V Vdd = 0V
2. Input voltage from 555 is 0-5 V
3. Arbitrary low and high thressholds of 1V and 3V
Then using R1/R2 = (Vth-Vtl)/(Vcc-Vdd) = 2/5 = 0.4
I arbitrarily chose two resistors that met the 0.4 ratio - 1,000 and 2,700 ohms
Then using Vref = Vth*R2 + Vtl*R1 / (R1+R2) = 3*2700 + 1*1000 / 3700 = 2.5V
Then calculating a voltage divider to generate the 2.5V reference voltage on "-" (easiest part, 10K each)
So here's the circuit, and when I breadboarded it, it seems to work fine.
Questions:
1. Is this the way you do it?
2. Are there any subtlties that I have missed?
3. How do you select the feed back resistor?
__I see many 1meg feedback resistors in circuits, but I don't know why. Mine's only 2.7k
__Any insight there?
Again, I thank you in advance.
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