Building a 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.
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.
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.
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
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 ?
Controllable via a USB connection from a serial terminal screen.
Greg (Barbouri)
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
Richard
Hi Richard,
I used the Sparkfun.com 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)
Thanks Greg,
Can I also confirm the 16x2 RGB backlit LCD?
I found this on Sparkfun: https://www.sparkfun.com/products/10862
or this on PiHut which looks more like yours :
https://thepihut.com/products/rgb-backlight-positive-lcd-16x2-extras
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!
Cheers
Richard
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)
Thank you Greg for the Schaeffer-AG link.
That works for pricing!
Richard