+/-3.5v to 0-100k resistance conversion circuit help please!

djpubba · Jan 9, 2006

I didn't have a 4.7k handy so I used two 10k to get 5k for R5. With that I can get down to 40 or so.

Adding R8 and R9 as you suggest, the max I can get to the right is 460.

Edit: However, even with R8 and R9 disconnected, chaging R5 to 5k brings the max for the far right down to 680. R8 and R9 brings it down even lower.

I have a feeling that even if we get 000 on the far left and 999 on the far right, center is going to be somewhere down around 150 and no amount of adjusting those resistor values will put it near 500 without the left or the right being way off.

ljcox · Jan 9, 2006

Try R5 = 3.3k (or 3 10 ks in parallel) To shift to the left, you need more current into the computer which means less resistance in R1 + R5.

I thought you said earlier that you had a large range on the right, but apparently not.

I'll do some calculations and post later.

ljcox · Jan 9, 2006

Here is an alternative. The pot (R10) will set the minimum voltage for both circuits.

Set R1 as before and set R10 for 999

djpubba · Jan 9, 2006

ljcox said:
Try R5 = 3.3k (or 3 10 ks in parallel) To shift to the left, you need more current into the computer which means less resistance in R1 + R5.

That gets the right side down to 032, with 057 for center and 495 for the right side.

I thought you said earlier that you had a large range on the right, but apparently not.

Sorry about that. That was with R1 incorrectly set around 22k to get the center at 500.

Here is an alternative. The pot (R10) will set the minimum voltage for both circuits.

With this change and the pot at it's max of 2k, we get 031 on the right, 048 at center and 136 on the far left. So we're going the wrong way.

ljcox · Jan 9, 2006

djpubba said:
That gets the right side down to 032, with 057 for center and 495 for the right side. So you need to reduce R5 further. We should be able to fix the right side by other means.

ljcox said:

Here is an alternative. The pot (R10) will set the minimum voltage for both circuits.

Click to expand...

With this change and the pot at it's max of 2k, we get 031 on the right, 048 at center and 136 on the far left. So we're going the wrong way.

Click to expand...

Yes, I realised that and just came back to delete the circuit. I had my thinking reversed.

When you post results, please include the voltage at the base of Q1 and the respective screen deflection.

What I am not sure about is the base voltage necessary to give 000.

ljcox · Jan 9, 2006

djpubba said:
ljcox said:

Then repeat the voltage & current measurements for 000 I can only get it down to 90, which is probably good enough) 4.06v / 347 µA 500 1.17v / 61.4 µA and 999 0.85v / 31.2 µA.

Then turn the power off and measure the resistance of R1. 157 ohm (as low as it will go)

Click to expand...

Are the voltages in red measured on the the base or the emitter of Q1?

djpubba · Jan 9, 2006

I'm thinking it's not so important to get it right at 000. The way the game software works is that you can calibrate your stick by moving it to upper left and lower right corners to set the min and max range and it'll pick the middle of those values for center. So it is not that important to reach 000 and 999. It is more important that we get it so we have 500 when R2 is centered and balance the two sides against that. i.e., 200 on the right, and 800 on the left (or whatever).

djpubba · Jan 9, 2006

ljcox said:
Are the voltages in red measured on the the base or the emitter of Q1?

The base.

ljcox · Jan 9, 2006

I am puzzled by the fact that you measured 0.85 V for 999 given that the maximum is 4.06 V.

4.06 V implies that R3 = 3.4 k, but 0.85 V min implies that R3 = 12 k. ???

They can't both be correct.

djpubba · Jan 9, 2006

The values I get on screen must be inverted.

ljcox · Jan 9, 2006

djpubba said:
The values I get on screen must be inverted.

I don't understand this point.

Perhaps it is time for you to provide a summary of the voltages, currents and screen deflections to clear up the confusion. Be sure to include the resistance values of the resistors & pots so we are all on the same wavelength.

Roff · Jan 9, 2006

Djpubba, I'm working on a better idea. How much room do you have for parts? :roll:

djpubba · Jan 9, 2006

ljcox said:
djpubba said:

The values I get on screen must be inverted.

Click to expand...

I don't understand this point.

Well, my measurements indicate that the lower the voltage, the higher the screen value is. You seem to expect the opposite, so the screen values must be inverted from what you're expecting.

Perhaps it is time for you to provide a summary of the voltages, currents and screen deflections to clear up the confusion. Be sure to include the resistance values of the resistors & pots so we are all on the same wavelength.

Sure. What configuration would you like me to take measurements from -- Ron's original configuration or Ron's + your suggested changes?

How much room do you have for parts?

About 4 square inches.

djpubba · Jan 9, 2006

I see now I misunderstood your point about the screen values.

ljcox · Jan 9, 2006

djpubba said:
ljcox said:

djpubba said:

The values I get on screen must be inverted.

Click to expand...

I don't understand this point.

Click to expand...

Well, my measurements indicate that the lower the voltage, the higher the screen value is. You seem to expect the opposite, so the screen values must be inverted from what you're expecting. No, see the spreadsheet below.

Perhaps it is time for you to provide a summary of the voltages, currents and screen deflections to clear up the confusion. Be sure to include the resistance values of the resistors & pots so we are all on the same wavelength.

Click to expand...

Sure. What configuration would you like me to take measurements from -- Ron's original configuration or Ron's + your suggested changes?
Ron's original but with R5 = 3.3k or lower. If not, 5 k will do.

As you can see, these are based on your measurements when R1 + R5 was set to about 32.5 k. The "I" value is calculated from the R5 and v figures. I deduced the R5 value from your current measurements.

I-----------------v------Def----------R5

106.5----------4.06----290---------32.5
61.8-----------2.609---500---------32.5
30.1-----------1.578---999---------32.5

uA-------------Volt------------------k Ohm

Roff · Jan 9, 2006

Djpubba, have you measured the voltages at the extreme ends of one (or both) of the pots in the original Vectrex controller, with no additional circuitry added? I tried to find them in this thread, but was not sure what I was reading. I think I can come up with something that works if you can post those voltages.

djpubba · Jan 9, 2006

Ron H said:
Djpubba, have you measured the voltages at the extreme ends of one (or both) of the pots in the original Vectrex controller, with no additional circuitry added? I tried to find them in this thread, but was not sure what I was reading. I think I can come up with something that works if you can post those voltages.

With nothing connected to the controller except +5 and ground,

Input at +5 pin = 4.94v
Output on X pin, stick far left = .768v
Output on X pin, stick centered = 2.538v
Output on X pin, stick far right = 4.00v

Measurements for Len coming next.

ljcox · Jan 9, 2006

A ha, I have been confusing left and right. 999 is far left and minimum voltage - correct? On re-reading the thread, you told me this, but I've had it in mind that 000 was far left.

Roff · Jan 9, 2006

I tweaked this by assuming the monostable element in the computer is similar to CD4538, where the pulse width=RC. Also, I assumed that the resistance varies about 46:1 (102.2k:2.2k).
The controls may be backward, as you may have discovered. If so, we'll tackle that next. :cry:
The nominal values were fine-tuned by simulating, so the actual values can be somewhat different - hence the pots.
Unfortunately, this design will be sensitive to VCC(+5V) variations with time, temperature, individual computer's actual VCC value, and phase of the moon. We might be able to minimize this if you have room for more parts, like an op amp or two and more resistors.

PS calculated min and max currents are 22ua and 1.022ma, respectively.

djpubba · Jan 9, 2006

Measurements for Len:

With R5 at 3k

screen - Q1 base voltage - Q2 current
031 - 4.04v - 1 mA - far right
054 - 2.546v - .5 mA - center
454 - 0.778v - 69.2 µA - far left

With R5 at 5k

screen - Q1 base voltage - Q2 current
046 - 4.05v - .6 mA - far right
082 - 2.49v - 386.7 µA - center
645 - 0.779v - 48.3 µA - far left

With R5 at 10k

screen - Q1 base voltage - Q2 current
089 - 4.05v - .346.1 µA - far right
155 - 2.49v - 199.4 µA - center
999+ - 0.779v - 26.4 µA - far left

+/-3.5v to 0-100k resistance conversion circuit help please!

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