Analog Votage to 4 Digit Seven Segment Display

[StudentSA]

Good Day

I have an analog voltage ranging from 0V - 5V I would like to display a value between 0 and 9999 depending on the voltage level i.e. 0V = 0 on display and 5V = 9999 on display.

What is the best way to achive this WITHOUT the use of a microcontroller?

I was thinking of implementing a Voltage to Frequency (V-F) convertor followed into a counter that is configured for a specific reset/latch period?

Any further suggestions will be appreciated.

Regards,
StudentSA

 

[ericgibbs]

Good Day

I have an analog voltage ranging from 0V - 5V I would like to display a value between 0 and 9999 depending on the voltage level i.e. 0V = 0 on display and 5V = 9999 on display.

What is the best way to achive this WITHOUT the use of a microcontroller?

I was thinking of implementing a Voltage to Frequency (V-F) convertor followed into a counter that is configured for a specific reset/latch period?

Any further suggestions will be appreciated.

Regards,
StudentSA

hi,
I would think that for 9999 display a V2F with say a 0.1sec gate for a 10kHz clock would be the easiest way.

 

[StudentSA]

Hi,

Could you please elaborate on gate and clock?
Is gate your refresh rate? and clock the maximum frequency from the V-F?
If this is the case you probably meant a 100Khz clock?

Regards,
StudentSA

 

[MrAl]

Hi there,


We also need to know what kind of accuracy you are after.
For example, if the reading was 9999 and the voltage was really 4.90v instead of a perfect 5.00v, would that be ok or not?

 

[StudentSA]

Accuracy is not of primary concern 5-10% or less would be preferable

 

[ericgibbs]

Hi,

Could you please elaborate on gate and clock?
Is gate your refresh rate? and clock the maximum frequency from the V-F?
If this is the case you probably meant a 100Khz clock?

Regards,
StudentSA

Hi
I should have typed 1sec clock.
The V2F's will run at 100kHz is you want a 0.1Sec refresh rate for the display.

The gate is a logic gate that is opened for 1sec [or 0.1sec], during the 1sec period a counter is clocked with the pulses from the V2F. After 1sec the count is transferred to the display buffers then clear in say 100uS.
The gate/count then resumes....OK.?

 

[StudentSA]

To clarify the concept please refer to the following figure

 

[StudentSA]

Hi,

Thanks Eric, yes that clarifies things. I will try to implement something along this concept.

Regards,
StudentSA

 

[ericgibbs]

To clarify the concept please refer to the following figure

hi,
This is the way.
A little logic will supply the Gate period/Latch/Reset

 

[StudentSA]

Okay... so I have managed to source an awsome old IC the MMC22925 This is a 4 digit counter IC with multiplex display driver supporting 4 digit display.

SO... based on previous. I need to latch the value to the display and reset (refresh rate) the count. I have come up with this circuit concept.

excuse the epic artwork




I need to latch the counted value by supplying a low signal. even though I hold the signal low it will keep the value when the signal went low (falling edge triggered)

however Once latched I need to reset the internal counter, BUT reset needs a small time delay after a latch so I implemented a capacitor timer to cause the 556B to trigger later on falling edge of capacitor.

The capacitor is designed with RC = 33us so it will charge competely in the 556A output high via transistor (2N2222 acting as a switch).
When 556A goes low the capacitor will discharge and trigger the 556B in 1RC time (33us).
This will inturn output our reset pulse.

this should hopefully work?

 

[ericgibbs]

hi,
Your Latch/Reset signals have to be synchronised to the 0.1s [0r 1sec] pulse frequency input gate.
So gate open for say 1second, accumulate a count, end of the 1 sec gate Latch the data then reset the counter, then reopen the gate for the next measurement.

 

[StudentSA]

This is exactly what the above described circuit does... It has a period of 0.1 seconds and uses only a few microseconds at the begining to latch and reset. The majority of the period is used to count.

The latch/reset signals cannot be syncronized as the chip requires a small "settling time" between these signals.

 

[MrAl]

Hi,


I forgot to mention that i had made this very thing back in the early 1980's, but i forgot what the part number was for the frequency to voltage chip. It was something like 9400 or something like that, and was fairly stable for that kind of device back then. I was able to get about 5 digits, but the stability of the rightmost digit wasnt super good and would change quite often. It will probably be good enough for your app though.
Oh yeah, the way i did it was to simply use a frequency counter with the v to f chip, an 8 digit unit i had built out of discreet 7400 family counters and latches and other devices. The LED display was rather smallish, but it did the trick. I actually still have this thing around (the chip somewhere too) and just checked it the other day to make sure it was still working (i needed a crystal controlled output from it for testing something else too).

 

[Reloadron]

I also did one in the early 80s and as MrAl mentioned the chip used was a FV9400 which could do Frequency to Voltage or Voltage to Frequency. I then used a pair of BCD Counters (3 Digit) that were MC14553 chips and the display drivers were MC14543 chips. The exact circuit ran in the old Radio Shack Engineers Notebooks 1 & 2 by Forrest M. Mims III.

The little circuit that took care of the gate and latch signals was like the image I am posting. This should be what you want to get going. I also hope it works as trying to upload files from work on a secure system doesn't always work for me. If not I'll post the circuit later.

Ron

 

[MrAl]

Hi Ron,


Oh ok good. Interesting, i think i have that exact same chip i used way back then laying around some place ha ha. Not just the same part number, but the actual same exact chip itself.

 

[ravikarti]

Hi StudentSA

I am also making a similar circuit. Can u share some of the details of ur V2F circuit. I have made one using an Op-amp oscillator circuit. But the voltage freq relation is not linear.

Also can u share ur circuits on configuring the counter for timed latching and enabling. I know that we have to enable and disable the counter for an exact period of time so that the counter will count at the V2F freq output for the specified time and give a suitable number output. How can we calculate tht with sufficient linearity.???

Pls help

 

[Reloadron]

Hi StudentSA

I am also making a similar circuit. Can u share some of the details of ur V2F circuit. I have made one using an Op-amp oscillator circuit. But the voltage freq relation is not linear.

Also can u share ur circuits on configuring the counter for timed latching and enabling. I know that we have to enable and disable the counter for an exact period of time so that the counter will count at the V2F freq output for the specified time and give a suitable number output. How can we calculate tht with sufficient linearity.???

Pls help

First, if you look a few post up in this thread I posted the circuit that will take care of gating your counter, I posted the same circuit in the other thread you posted in. I suggest you look at the circuit(s) and understand how they work.

Next, though the 555 will work as a V to F converter it is not a good choice and is only linear through a small range. A much better chip is a chip designed as a V to F or F to V like this chip.

Neither of your post on this subject mention the circuit you are using. People have no clue as to the voltage range you are working with from the thermistor. Posting a schematic would greatly help you get some help.

Ron

 

[hkBattousai]

I your voltage range was between -1.999V and +1.999V you could have used 7107.

ICL7107 / ICL7106 Digital LED Ammeter (Ampere Meter)