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RadManCF

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Back in college, I minored in physics, and while taking Linear Integrated Circuits, I became interested in using analog circuits for control purposes. Has anyone here attempted to use an analog circuit for rocketry applications? I had an idea for a timer, using a temp dependant resistor, a potentiometer, and a zener diode. The pot and the temp dependant resistor are placed in series, with the pot first. The zener diode is attatched between the pot and resistor, reverse biased. As the resistor heats up, the resistance rises, and the voltage at the node between the three components rises, until the zener voltage is reached, and the zener diode begins passing current, which can then do whatever. Any thoughts?
 
Back in college, I minored in physics, and while taking Linear Integrated Circuits, I became interested in using analog circuits for control purposes. Has anyone here attempted to use an analog circuit for rocketry applications? I had an idea for a timer, using a temp dependant resistor, a potentiometer, and a zener diode. The pot and the temp dependant resistor are placed in series, with the pot first. The zener diode is attatched between the pot and resistor, reverse biased. As the resistor heats up, the resistance rises, and the voltage at the node between the three components rises, until the zener voltage is reached, and the zen;er diode begins passing current, which can then do whatever. Any thoughts?

Sounds like an experiment is in order. The premise sounds reasonable to me.
 
Performance will obviously vary over temperature which in most cases is a big problem.

Zener diode conduction is not like a switch. Below the Zener voltage there will not be much current and as you approach it the current increases.

You can do a lot better with a simple RC circuit and you can select parts with good performance over temperature.

If you want to play with analog circuits I highly recommend getting some variant of SPICE. I currently use LTSpice which is a big improvement over what I started with a couple decades ago. Instead of drawing a circuit and labeling the nodes by hand it includes a schematic capture tool.
 
Performance will obviously vary over temperature which in most cases is a big problem.

Zener diode conduction is not like a switch. Below the Zener voltage there will not be much current and as you approach it the current increases.

You can do a lot better with a simple RC circuit and you can select parts with good performance over temperature.

If you want to play with analog circuits I highly recommend getting some variant of SPICE. I currently use LTSpice which is a big improvement over what I started with a couple decades ago. Instead of drawing a circuit and labeling the nodes by hand it includes a schematic capture tool.

I've used PSPICE before, is that much different?
 
I've used PSPICE before, is that much different?

PSPICE is a moving target (the first edition for the IBM PC was released wayback in 1984) so I can't say. My experiance with PSPICE is not at all recent. Follow the link, read, download, and play. It is free.
 
Sounds interesting... keep us posted...

Im not sure why you are trying to build a temperature driven timer though. It will be subject to errors and uncertainty.

As UhClem says an RC network is the classic approach. You should be able to build a timer using little more than a resistor, capacitor, and transistor.

I posted a simple OpAmp driven RC network in another thread recently:
https://www.spiegl.org/rocket/timer/circuit.html


-->MCS


.
 
Sounds interesting... keep us posted...

Im not sure why you are trying to build a temperature driven timer though. It will be subject to errors and uncertainty.

As UhClem says an RC network is the classic approach. You should be able to build a timer using little more than a resistor, capacitor, and transistor.

I posted a simple OpAmp driven RC network in another thread recently:
https://www.spiegl.org/rocket/timer/circuit.html


-->MCS


.
The reason for a temperature driven timer was that I was learning electronics from and with physicists who have a tendancy to reinvent the wheel. Using a temp dependant resistor in a voltage divider with a zener diode was the first thing that occurred to me. In each of my electronics classes, we had to do a project at the end of the semester, making a circuit, documenting it, etc. I had considered developing this citcuit in linear circuits, but decided not to, as that class is so focused on op amps. I ended up building a circuit for controling the angular position of a shaft, using an inverting op amp, a non inverting op amp, which both fed a summer. A series of potentiometers were placed on the shaft, and these were used in the inverting and non inverting op amps. A second set of potentiometers was used to control the setpoint of the system. The output of this circuit was sent to a motor control circuit. The logic portion of the circuit worked quite nicely, the output voltage from it responded to changes in the position of the pots exactly as it was supposed to. What didn't work was the motor control. We were taught next to nothing about electric motors, and so we were pretty much just guessing about how to control it. The transistors we used for the output also turned out to be undersized, and rendered the motor control circuit to be more useful as a firelighter than as a motor control.
 
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