# ramp time to voltage

Discussion in 'Electronic Design' started by [email protected], Apr 28, 2005.

1. ### Guest

I have a bunch of x y flatbed recorders and I want a simple rising
volatge to simulate passing time on the x axes. I can work from a
diagram and know some basics. HP made this in a small package.... HP
17108A.... anybody have one?
I can take MV or volts 1-10.

2. ### Dan HollandsGuest

Two approaches of many

1. Use a binary counter with appropriate weighted summing resistors
connected to the outputs
Adjusting the clock rate into the counter determines the rate of rise. The
number of stages in the counter determines the resolution.

2 Use a microcontroller with an analog output such as Analog Devices ADUC812

--

Dan Hollands
1120 S Creek Dr
Webster NY 14580
585-872-2606

www.QuickScoreRace.com

4. ### Spehro PefhanyGuest

Dual 12-bit voltage-output DACs. One of the few with such a
peripheral, but rather slow and power-hungry.

Best regards,
Spehro Pefhany

6. ### RockGuest

You could keep it simple by using an LM334 constant current IC (3 pin
device) by National and discharge it into a capacitor. You can tweak
the current on the LM334 with a pot, and make a nice linear ramp. This
is a 3 part solution, not including any power supply.

Rocky

7. ### John PopelishGuest

Add an opamp to make an integrator and you get a buffered output.

8. ### Guest

Thanks everybody, most of you are over my head. I would like at least
one hour at one shot. I would like a diagram,( I could build heath
kits) I'm not in the electronics trade.

9. ### John LarkinGuest

Most of the flatbeds had high (often infinite) input impedance on the
low voltage ranges. So a simple resistor-capacitor will make a nice
ramp.

So,

*--------100K res------10meg pot----------*--------*---------to recorder+
| | |
| | |
+ | + |
9v battery capacitor switch
- | - |
| | |
| | |
*-----------------------------------------*--------*--------- recorder -

The capacitor size depends on how fast you want to sweep and which
range of the recorder you're on. Try 10 microfarads to start, 1 volt
range maybe. Stay at 1 volt range or preferably less, otherwise the
sweep will get nonlinear.

Open the switch to run the ramp.

Ignore all the complicated electronics suggestions.

John

10. ### Jim ThompsonGuest

And that guy behind the curtain ;-)

...Jim Thompson

11. ### Spehro PefhanyGuest

For one hour, you'll probably do best with a CMOS 555 feeding a
74HC4040 feeding a R-2R ladder network. Maybe someone feels like
drawing it up.

Best regards,
Spehro Pefhany

12. ### Jonathan WesthuesGuest

He said "an hour at one shot". 3600 uF cap or giga-ohm resistors?

I would say attach the minute hand of a clock to a rotary pot; use a
multi-turn pot for a multi-hour delay.

Jonathan
http://cq.cx/

13. ### JoergGuest

Hello Dan,
Or a DAC08, or two of them for more precision. These should be found in
the bins of any decent lab and would save a lot of resistor matching and
soldering.

Regards, Joerg

14. ### JoergGuest

Hello,
If you are in a lab look around whether one of the function generators
allows for really long timing. Sometimes they will indicate in
"milli-Hertz", sometimes as period times. Only digitally controlled ones
will be able to do that. That way you may not have to build anything.

Regards, Joerg

15. ### Fred BloggsGuest

Will this be running off the line? Maybe two opamps and an 6-bit counter
at the core...Do you know enough to build a small DC power supply, or
any other construction techniques?

16. ### John LarkinGuest

10,000 uF isn't a huge cap. Or use one of those 0.47F ultracaps.

John

17. ### Jonathan WesthuesGuest

How fast will that 0.010 F electrolytic self-discharge? The tolerance will
not be so nice either.

I see a lot of +80%/-20% with the double-layer capacitors. A mechanical
clock and a pot would be much more accurate. The error is all due to the
nonlinearity of the pot, and that doesn't accumulate. Or use a PIC.

Jonathan
http://cq.cx/

18. ### Ken SmithGuest

I suspect it would be easier to find a complete DAC than an R-2R ladder,
but the idea is a very good one.

19. ### Guest

Thanks John, NOW, I understand.

20. ### Guest

The flatbed is line voltage. I can build but not design. Can do vdc.
Is a discharging cap more linear? I can run my flat bed x axis
backwards if this helps.