Line detection/electronics help

[compton_effect]

I'm in an electronics class in which we build a sumo bot for our final project. Right now I'm working on the line detection using QRD1114 photo emitters/detectors. The problem is that the transistor is outputting about 2.4 volts (low) and 4.6 volts (high) on a 5 volt input, which is borderline for inputting into the LS family digital logic.

I received a suggestion that I should use an LM741 op-amp with a low gain (~10) and tie 2.4 volts to the offset, so it nulls the low input and amplifies the high to the 5V rail. On the 741, there are two offset nulls, though I'm not exactly sure how to null out a 2.4 volt signal. Can anyone give any suggestions as to how to achieve this or possibly a better way to approach this problem? Thanks.

 

[berkeman]

What supply rails do you have available? Probably the best way to process the output of the photo sensor would be to use a single-supply comparator, with its reference set between the high and low output voltages of the sensor. Be sure to include some hysteresis in the + feedback path of the comparator.

 

[ravenprp]

Hi there,

It sounds like you are facing a common issue in electronics projects - getting the desired output voltage from your components. In this case, the transistor is outputting a voltage that is borderline for your digital logic input. The suggestion to use an LM741 op-amp with a low gain and offset nulls is a good one. However, if you are not familiar with how to null out a specific voltage, it can be a bit tricky.

One way to approach this is to use a voltage divider circuit to reduce the 2.4V signal to a lower value that can be easily nullified by the op-amp. You can use two resistors in series, with the 2.4V signal connected to the junction between them. By choosing the right values for the resistors, you can create a voltage divider that outputs a lower voltage, such as 0.24V or 0.24V, which can then be easily nullified by the op-amp.

Another approach could be to use a potentiometer in the feedback loop of the op-amp, which allows you to adjust the gain and null out the 2.4V signal. This would require some experimentation and fine-tuning, but it can be an effective solution.

Lastly, you may want to consider using a different transistor or a different type of photo emitter/detector that can provide a more suitable output voltage for your digital logic input. Sometimes, changing the component can be a simpler and more effective solution.

I hope this helps and good luck with your project!