Tiny display needed

[GH Crash]

Hunting for any and all help I can get.

I'm wanting to design a small circuit that uses a digital potentiometer in place of a mechanical one but I can't come up with a tiny (fit-on-the-board) display that will give me some indication of the wiper position of the digital pot. Any suggestion for a simple means of indicating wiper position for the digital pot?

I'm greatly restricted in the total area for the circuit board. The digital pot, its push button adjustment and whatever display needs to fit on a one by two inch board. Any type of display, volts, amps, resistance, just something that give indication of the wiper position would be good.

Displays that require a complex wired control board are probably outside my abilities. I know nothing about electronics or circuit design. I'm reasonably good at reading a circuit diagram and soldering tiny components onto a circuit board.

Any help, advice or suggestions you might have would be greatly appreciated.

 

[danadak]

Tiny LCD :

https://www.aliexpress.us/w/wholesale-tiny-lcd.html?spm=a2g0o.home.search.0

Regards, Dana.

 

[Ian Rogers]

Just search "0.49 inch ssd1306" 4 wires but you'll need a micro. a tiny pic will do the job.

Otherwise google mini volt meter and convert the circuit to read in volts.

 

[rjenkinsgb]

0.96" OLED displays are common, easy to use and quite cheap.
eg.

0.96" OLED Display Module (128x64)

This is a simple, affordable OLED display module to add to your projects using your favourite microcontroller. This 0.96" OLED has a 128x64 resolution and is driven by the popular SSD1306 using I2C for communication with your microcontroller - meaning it will work for lots of code libraries for...

thepihut.com

Other than that, there is a 0.42" one - but around 4x the cost:

World's Smallest 0.32" OLED 60x32 Display Screen by Questwise Ventures on Tindie

Measures only 11.5 x 11.5 x 2.4mm, probably the smallest on the market! Has castellated pads and works with I2C

www.tindie.com

Those do need a microprocessor to drive them..

This is pretty much the smallest voltmeter module I can find:

Mini 3-wire Volt Meter (0 - 99.9VDC)

Put a voltage meter anywhere with this very handy display. These are often used by RC hobbyists for keeping track of batteries but we thought it would be great on a breadboard or enclosure. This is the 3-wire version of the volt meter, two wires are used to power it and the third wire is used...

thepihut.com

Cut off the mounting ears and it looks to be about 1" wide.

 

[aliarifat794]

OLED is coming to my mind. https://www.waveshare.com/product/displays/oled/0.96inch-oled-b.htm

 

[zahwi]

You can use LED bar graph driven by LM3915 and digital pot IC like X9C104 that adjusting pot by up/down buttons. You need some electronic knowledge to connect the ICs.

​

 

[alec_t]

driven by LM3915

If you want a logarithmic response and if you can source a LM3915 (which is now obsolete).

 

[ZipZapOuch]

If you want a logarithmic response and if you can source a LM3915 (which is now obsolete).

Does the OP have a log digital pot? How would a log LM3915 help him display the approximate wiper position of a log pot? What is the transfer function for how I see the knob position vs the 10 lights in the display if the potentiometer is linear but the LM3915 is log? Likewise, if the potentiometer is log but my visualization of a potentiometer knob is pretty linear (1/4turn, 1/2 turn, 3/4turn, full blast). I'd like to see what constitutes half way.

 

[GH Crash]

Man!!! I never expected such a response.

Give me a day or two to investigate/digest all this good information.

 

[GH Crash]

ZipZapOuch, the digital pot is linear.

Right now, after all the good information about micro displays, I'm really struggling with the control side. I have no idea which/what controller is need for the different displays. It also sounds like some form of programming will need to be done. That is way beyond my abilities.

 

[ZipZapOuch]

ZipZapOuch, the digital pot is linear.

Right now, after all the good information about micro displays, I'm really struggling with the control side. I have no idea which/what controller is need for the different displays. It also sounds like some form of programming will need to be done. That is way beyond my abilities.

A single chip, LM3914 will light a "bar graph" of 10 LEDs. Small LEDs or even complete bar graph arrays can be purchase. A few small resistors are all that is needed to convert your analog voltage to light from zero to 10 LEDs of the array to give you an idea of your wiper position.

https://www.mouser.com/c/semiconductors/driver-ics/led-lighting-drivers/?m=Texas%20Instruments&series=LM3914&utm_id=179597776&gad_source=1&gbraid=0AAAAADn_wf0NrJ7Y8lh4_Z1KGD0r_1Z2T&gclid=CjwKCAjwqMO0BhA8EiwAFTLgIJSbaHjBxbQEeid80v3wPHPK-Q9W1W_SaezPJ7ZdI6jWAYW-hHmdjxoC_A8QAvD_BwE

You may be able to find some new-old-stock in a standard DIP through-hole package size but the one in the link is the only version still in production.

 

[crutschow]

design a small circuit that uses a digital potentiometer

How will you control the digital pot (what signal format)?

 

[GH Crash]

Crutschow, the digital pot that I'm using is the Renesas X9511. It is push button (momentary contact) controlled with 32 wiper tap points.

ZipZapOuch, I hadn't thought of using a light bar. Thanks for the suggestion. I like its simplicity. I will investigate that approach some more.

I originally was thinking along the lines of a digital display because I wanted the flexibility to display the wiper position regardless of using a 32-tap digital pot or one with 64 wiper taps. I noticed that the bar graphs could be cascaded but that takes room on the limited area circuit board.

 

[rjenkinsgb]

What is the digital pot going to be used for?

If it is anything other than producing a voltage "tap" from fixed supply (eg with the VH & VL connected to such as 5V or 3.3V and ground), you cannot really measure the pot position.

ie. If it is being used for such as an audio volume control, with a signal passing through it, you cannot measure or monitor it.
The only way to track it for that type of use would be to have an external microcontroller that takes the up & down signals, drives the display part, stores the last position while power is off, and operates the digital pot as a slave device.

 

[GH Crash]

The pot is being used to replace a mechanical pot. (Accuracy and repeatability of the mech pot was unsatisfactory.) The pot is used to generate an input signal to an ATTiny85 chip that provide a PWM style speed control to a small DC motor. In essence, it is acting as a voltage tap. The ATTiny85 compares the wiper voltage to system voltage to generate the pulse width parameters.

The in-use process goes something like this.
1. The pot wiper position is set. (This is the point that I want to monitor)
2. The pot is then connected to the ATtiny85 and the 85 is energized. (No monitoring)
3. The 85 reads wiper voltage/position and stores the value.
4. The pot is then disconnected.

The pot's resistor element's wiper is not being 'used' for anything during the process of setting it (step 1 above) therefore reading volts, or resistance, at the resistor endpoint and at the wiper should be possible. Monitor after the pot is connected to the 85 chip would be worthless even if it was possible. The readings at that point would be ATtiny85 condition, not the pot.

Ideally, I would like have indication of the pot's wiper position, either as an absolute value or as ratio of wiper position to total travel. The first step is to find (learn about) a display system (display and driver) that meets the small size and simplicity restrictions that are due to circuit board size and my lack of knowledge.

Again, all comments and suggestion are greatly appreciated.

GH

 

[rjenkinsgb]

The pot is used to generate an input signal to an ATTiny85 chip that provide a PWM style speed control to a small DC motor. In essence, it is acting as a voltage tap.

OK, that's fine!

A voltmeter, either digital or bargraph style, would be the simplest position indicator.

If you use one of the small, three digit modules, those apparently autoscale - so feeding 0-1V should display 0 - 100 (actually 1.00), so a direct percentage of the wiper position or target PWM.

 

[GH Crash]

I agree that one of the 3-digit voltmeters would work. Except for this project they have two undesirable characteristics; they are not SMD/SMT and their size. Remember that the circuit board is restricted to 1x2 inches. Several of the aliexpress displays that danadak recommended are about the right size but I can't find information on driver of circuit requirements.

I'm going to spend about another week searching for a suitable display and driver. If nothing suitable can be found in that time, I will go with a no-display circuit design and, at a later date, re-design the digital pot circuit to accommodate a display.

Your help, regardless of whether a suitable display is found, has helped me greatly. I know that several of you have put in quite a bit of effort in trying to help me.

 

[rjenkinsgb]

For info, the "bare glass" LCDs need a specialised drive system using multi-level signals.

A TFT or OLED display with four (or few) pins has the complex drive IC included, and can work with a small surface mount MCU.

This appears to be the smallest & cheapest practical display on there:

https://www.aliexpress.us/item/1005004502926458.html

 

[Ian Rogers]

If you do go for a lil tiny micro and the I2C 0.42" LCD then all the drivers will be found on the arduino system

You won't have to do much other than read the feedback, then monitor and change the pot value.

I should imagine the tiny micro could be hot glued to the display so all you need is a pin connected to the "feed back" voltage and the two or three wires to the digital pot.

 

[ChrisP58]

I don't think that you need the pot.

Just run your two up/down buttons directly into the ATTiny85. Have your code increment/decrement an internal register. And use that value to feed your display and to calculate your PWM timing.

Using this plan, you now have up to 256 levels for the count/PWM instead of the 32 that your pot has.

The ATTiny85 does have EEPROM so you can save the counter value and restore it at power up.