Alarmish circuit design

[bbkg]

Can any one help me with this?

A new COVID-19 “fictional” vaccine will be available at the end of April 2021. The vaccine MUST BE stored between -20˚C and 10˚C. You are tasked with designing, simulating, and breadboarding a storage temperature monitoring device that will produce an alarm if the temperature exceeds the storage temperature range. It has also been requested to add a “test” feature that the user has available which verifies the operation of the device. The following components MUST BE included as a functional portion of the design, meaning that each part contributes to the functionality of the final design:

1. Must include at least two of following (they can be two of the same component):

a. LM741

b. AD712

c. Diode (any type)

d. BJT Transistor

e. MOSFET Transistor

2. NTCLE100E3101GB0 (THERMISTOR NTC 100OHM 3560K BEAD).

NOTE: You will NOT actually use the component. This component can be simulated using a variety of methods. DO NOT go out and purchase the thermistor. It is not necessary!

 

[betwixt]

NOTE: You will NOT actually use the component.

That's a relief, using 40+ year old ICs isn't a good idea for modern medical equipment, even if it is fictional!

You can do this with just the LM741 wired as a comparator with hysteresis, the thermistor to actually sense the temperature and maybe two transistors if the alarm has to be from an oscillator.

Personally, in view of the wide span between upper and lower temperatures, I would use a window comparator (two LM741s), it would be more practical than expecting hysteresis to be accurate on such an old device.

Brian.

 

[d123]

Hi,

Yes, a window comparator is a good choice.

How could testing functionality be ensured if no PCB 'insta-adjust' onboard fridge/freezer (!) available...? Maybe, if thermistor -20 and +10°C voltages are known and reliable values, a voltage reference with resistive divider ladder fed to window comparator via a test pushbutton. How to switch from real to test signal without distorting either signal or compensating for unavoidable switch voltage drop is another headache to consider. Simplistic suggestion.

 

[betwixt]

I would also point out that the thermistor type isn't a good choice, especially at the low end of the measurements because it's low value will inevitably result in considerable self heating. For simulation purposes it should be adequate though.

Brian.

 

[bbkg]

Thank you Guys, I figured it out. Yes, I will use a window comparator, with the simulated thermistor circuit being used as the input. Then connect the output from the two comparator to a and gate using two transistors. Et voilà. Thank you so much to all of you.

 

[d123]

Thank you Guys, I figured it out. Yes, I will use a window comparator, with the simulated thermistor circuit being used as the input. Then connect the output from the two comparator to a and gate using two transistors. Et voilà. Thank you so much to all of you.

Hi,

How's it going? Is the circuit/simulation working?

Is there a schematic yet? - I ask as I can't visualize that part of the circuit or how the AND is set up to be high or low regarding temperature limits (bold part of your reply).

Something has been troubling me/on my mind about your circuit for a few days. I recollect, may have only been one circuit I tried a few years ago, and specifically my naïve configuration, that op amps as window comparators on a single supply have an output low that is mid-supply - perhaps as one sinks while the other sources or something.

Goggled the topic a few days ago but woeful lack of 'op amp window comparator' discussions found, much less application notes, only this came up:

How to Build a Window Comparator Circuit

Assume diodes are for that reason. Note author seems honest, not faking expertise, nice: see last two paragraphs...

Hope all is going well with the alarm circuit.

 

[bbkg]

I was able to do it. works as expected. I made few adjustments.

 

[KlausST]

Hi,

The circuit
* violates power supply range
* violates common mode input voltage range
* can not drive useful LED current
* uses a questionable 800V diode in a 5V node
I'd say the circuit can not work at all.

The chart on the right just shows the R1 power dissipation ... and has nothing to do with any Opamp function.

Klaus