I am experimenting with a HB100 to determine velocity of objects and was going to build an amplifier which I don't have a lot experience completing. I have found different designs online and was going to use the design proposed by jim-p HB100 Amplifier. Two questions I had:
The LM358 op amp is described as inexpensive but noisy and I was going to substitute a TL072. It inexpensive, easy to obtain and is reportedly much less noisy. Any reason this would not be a good substitute?
The design in earlier post appears to use all ceramic capacitors. For the 4.7 uF capacitors I was going to substitute an aluminum electrolytic capacitor for the ceramic. Any reason this may cause a problem?
Am I interpreting the connections to the TL072 correctly? Pin diagram on schematic
Any suggestions would be appreciated. The proposed schematic and calculations are below. Thanks.
You mentioned a supply voltage of ±15 V is ideal. Will the 5 volt supply not be adequate? The data sheet appeared to indicate a wide range of input voltages, again I'm not familiar with op amps Thanks.
There won't be a lot of headroom with this non rail2rail opamp and a single 5volt supply
Input and output could easily clip. I expect that AC output voltage can't reach more than 1volt peak/peak.
Leo..
Is the reason the TL072 or LM358 will not work because of the higher required supply voltage or that they are single supply vs rail to rail. I would like to understand this better and appreciate the discussion and advice.
The output of common opamps can't fully swing to ground or VCC.
If you want 0-5volt output from an LM358, then it needs at least a 6.5volt supply.
The LM358 only has a positive-going output restriction (about VCC -1.5volt).
There are also input restrictions, both common- and differential mode.
Those restrictions can be found in the datasheet.
Leo..
An opamp with rail2rail outputs on a 5volt supply could output almost 0-5volt.
A non-rail2rail will only output 2-3volt.
Which could be a problem if you need to connect to an analogue input.
You would only use 20% of the range of the A/D.
Connecting to a digital input could also be a problem.
Switch points of a digital input are usually 30% and 60% (<1.5volt and > 3volt).
Leo..
The problem is with the common mode input voltage range.
Both the LM358 and the TL072 have smaller common mode input voltage ranges than the original LMV358, I show in my circuit.
After some reading its my understanding that the common mode input voltage range defines the input voltage of an op amp that will result in a linear amplification result. Input voltages outside of this range will result in a distorted amplification signal that can cause clipping and spiking. If counting the frequency will lead to an inaccurate count and with the HB100 inaccurate velocities. Single supply op amps generally will have a lower CMIV as opposed to rail to rail but even rail to rail have some limitations as how close you can get to each rail. If I'm reading the datasheets correctly for a 5v supply the CMIV for the LM358 is 0 to 3 v while the LMV358 is 0 to 4.8.
It's not my design. It's from an app note for a doppler radar module, that I can't seem to find right now.
However, it's just a very simple two stage amplifier using a single supply.
