Programmable Voltage Reference Case

Building a case for the
Programmable Voltage Reference project.
Case for the Programmable Voltage Reference project
Case for the Programmable Voltage Reference project

While wait­ing on the ver­sion 2.12 print­ed cir­cuit boards from OSH Park, I decid­ed to do some work on the case.
For con­sis­ten­cy I end­ed up using the same mod­el of Hammond enclo­sure that was used in sev­er­al pre­vi­ous projects. The mod­el 1455N1601 enclo­sure mea­sures 6.3″ L x 4.055″ W x  2.087″ H (160 x 103 x 53mm) and is made from extrud­ed alu­minum. The main body is an U shaped extru­sion with a flat extru­sion form­ing the top. The unit comes with 1.5mm alu­minum end plates, with a black plas­tic bezel that cov­ers the joint between the two alu­minum pieces.
I ordered a cus­tom front pan­el from Front Panel Express in the medi­um bronze anodized alu­minum, with a thick­ness of 2.5mm and an out­er bev­el of 1mm so that it would match the orig­i­nal 1.5mm pan­el depth of the plas­tic bezel.

Front panel with LED display, power switch, rotary encoder, and output jacks
Front pan­el with LED dis­play, pow­er switch, rotary encoder, and out­put jacks

The orig­i­nal Programmable Voltage Reference by uChip used a very small 4 dig­it 7 seg­ment HP bub­ble dis­play and a rotary encoder mount­ed on the board. The V2.12 board will have a remote dis­play, and a head­er for a RGB LED rotary encoder.
My plan is to mod­i­fy the alu­minum knob with a cen­ter light pipe to pro­vide a sta­tus indi­ca­tion of the cur­rent mode or error condition.

RGB LED rotary encoder with push button, mounted on a Sparkfun breakout board
RGB LED rotary encoder with push but­ton, mount­ed on a Sparkfun break­out board

I end­ed up with a bunch of blue 4 dig­it 7 seg­ment LED dis­plays from a recent Sparkfun sale. It should be real easy to see the cur­rent volt­age set­ting on the pan­el from across the room with these!
I put togeth­er an I2C inter­face board for these dis­plays based on a design by Adafruit, using a Holtek HT16K33 RAM Mapping 16*8 LED Controller Driver chip. A nice fea­ture of this chip is a dim­ming com­mand that pro­vides dis­play dim­ming in 1/16 incre­ments. I am think­ing of uti­liz­ing this fea­ture for sav­ing bat­tery pow­er after a set time, and have the dis­play resume nor­mal bright­ness after the rotary encoder has been moved, or it’s push but­ton pressed.
I made a bunch of these boards and will most like­ly use them in future projects.

7 segment 4 digit LED display I2C interface board. Front and back
7 seg­ment 4 dig­it LED dis­play I2C inter­face board. Front and back
Surface mount components and HT16K33 chip soldered to board
Surface mount com­po­nents and HT16K33 chip sol­dered to board
Back view of front panel
Back side view of assem­bled front pan­el with pow­er switch, rotary encoder assem­bly, out­put jacks, and dis­play assembly

The Programmable Voltage Reference case is most­ly ready, and I am now wait­ing for the main board to arrive in the next few days. I will doc­u­ment the build and post the final results in the near future.

7 Segment X4 I2C LED back­pack V1.0 Eagle CAD Zip files
OSH Park 7 seg­ment X4 I2C LED back­pack page

8 Replies to “Programmable Voltage Reference Case”

  1. yep, this too, much bet­ter than the board on it’s own — and a good dis­play too. any way to con­trol via pc or tablet ?

  2. Hi Greg, Yes I have popped up on this thread! Another ques­tion (sor­ry) is where did you source your 7 seg­ment dis­play? I naive­ly ordered one and it was just over an inch in length lol (I ordered it when I was very tired and for­got to look at dimensions).

    I uploaded the Front Panel Express lay­outs for both this and the mil­li­volt­meter pan­els and they end up being quite expen­sive (~$150 each). I would also get ham­mered import duty/VAT (being in the UK) .They are nice look­ing though and bet­ter than any­thing I could do on my 3D printer.

    Just to say the ser­vices at OSH are so easy and they are excel­lent. I don’t think we have any equiv­a­lent in the UK. I also notice they offer sten­cilling (for big­ger boards). Again, with FPE we do not seem to have a UK equiv­a­lent and I would prob­a­bly end up pay­ing a sim­i­lar amount to get cus­tomised pan­els from a UK spe­cial­ist manufacturer
    Best Regards

    1. Hi Richard,
      I used the 7‑Segment Display — 20mm (Blue), they also have Red and White in stock as of today.
      4x7 sege­ment dis­play blue Sparkfun

      I just checked my cur­rent pric­ing for the PVR pan­el, and it was just under $50 USD. Shipping can sig­nif­i­cant­ly increase the total price.
      Front Panel Express pric­ing for my updat­ed pro­to­type pan­el showed as $73.04 USD. A bit pri­cy, but they look so much bet­ter than my home­made panels.
      It looks like Schaeffer-AG which is a sis­ter com­pa­ny to FPE offers sim­i­lar ser­vices for Europe. Schaeffer-AG Front Panels

      I have been using OSH Park since 2012, and have always had great qual­i­ty boards and ser­vice from them. Highly recommended!

      Greg (Barbouri)

  3. Thanks Greg,
    Can I also con­firm the 16x2 RGB back­lit LCD?

    I found this on Sparkfun:

    or this on PiHut which looks more like yours :

    Actually I am real­ly get­ting into volt­age ref­er­ences and stan­dards. It sounds easy but can get very com­plex. I was read­ing about the LTZ1000 shunt. Maybe pair­ing that with a 24bit ADC (LTC2400 or bet­ter) would get you some­thing inter­est­ing. Just need an 8.5 dig­it DMM to test it!


    1. Richard,
      I use a RGB back­light neg­a­tive LCD dis­play, but the pos­i­tive units you list­ed will work also, just with dark char­ac­ters on a col­ored background.
      Adafruit Negative LCD RGB backlight

      Yes, the volt­age ref­er­ence, and pre­ci­sion mea­sure­ment quest can be a very deep rab­bit hole.
      The trick is to decide what you real­ly need, vs what would be real­ly impres­sive and cool to have.

      Greg (Barbouri)

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