New Phi-panel backpack PCB design and temporary price drop

Since its introduction, the phi-panel backpack has sold over 100 units. The sales has gone up especially recently. To meet the demands, I recently purchased/printed in large quantity ATMEGA328 chips and PCBs so I was able to adjust down the prices of various kits a few dollars each. I am hoping the price stays at this level from now on although I am saying “temporary”. The biggest challenges for this product are:

1) Finding LCDs that are low cost and good enough quality. I still can’t just order 100 LCDs at a time. That will last for a year 🙂

2) Competing against dummy “serial LCDs” with I2C port extenders. Those circuit components only cost dimes and the circuits are as dumb as a rock.

It is hard to show phi-panel’s quality with just the look or even a video. But I’m glad that almost everyone that purchased these backpacks are happy with their purchase and some said some very positive things about it. So to those happy customers, please tell your friends about this product. The more the demands, the lower the unit price may go, and the more features I will add to this line of product.

This new batch of PCBs feature a how row of ground connections. This will come in handy if you are using the 8-key firmware and laying out your own control panel. Each button will connect a button pin and one of the grounds. So I added a row of 8 grounds to cope with this. You don’t need to jam or twist 8 wires in one ground connection.

The various keypad layouts and face plates are arriving in a few days. It will be exciting!—phi-panel/

8 Responses to New Phi-panel backpack PCB design and temporary price drop

  1. liudr says:

    Regarding the 47 Ohm resistor, I am replacing the kits with 150 Ohm resistors, just to make sure the back light won’t be too bright.

  2. I’m planning on buying the Phi-panel backpack Kit + 20X4 display + keypad over on inmojo, but I have a couple questions.

    I looked, but couldn’t find, documentation on how to connect a buzzer and what specs for the buzzer I should buy. Is the buzzer connector the 2 pins next to the keypad connector labeled “S” and “-“? I looked in DigiKey at piezo buzzers, and there are lots of specs to narrow down a purchase. What specs (or manufacturer part number) do you recommend? Is there a part number on inmojo that I can use to purchase a known working buzzer model from your stock?

    I have a complex project that I need to be able to off-load as much processing from my UNOr3 as possible. Your Phi-panel seems to be the right solution for display and key-input. (I’m already using dedicated stepper driver IC and rotary encoder interpreter IC, and various serial to parallel ICs for LEDs and parallel to serial ICs for checking switch states to reduce needed pins, and only have 1 I/O pin left (after allocating serial pins for the Phi-Panel).


    • liudr says:


      Yes the S goes to + of the speaker and – goes to ground. You connect S to the plus of a speaker then the speaker – to a resistor and then to ground. If you order the back pack with one piece of this, I will include a speaker and a resistor for you.

      • Thank you for this offer. I just placed the order. The order number is 5384486 (I also included a note on the Pay Pal transaction identifying myself as well).

        Thank you again, and happy holidays.

      • liudr says:

        You are welcome Chris. I will ship your package tomorrow with a speaker and a 330 ohm resistor.

      • I got the kit today. Thank you for the Christmas present. 😀

      • liudr says:

        Alright! Have fun with the kit and happy holidays!

      • I have a couple build techniques that I used that you might want to share with other customers. I’d like to send you some pictures if you have an email address that I can contact you directly with. Email or FB message me using my forum contact info to get me your email if you don’t want to publicly announce it on this blog.

        I’ve been having a couple issues with the 1.5.1 and 1.6.2 firmwares using the big_show_NSS sketch on my UNOr3. I modified the sketch to change “NewSoftSerial” to “SoftwareSerial” because I’m using Arduino 1.0.3 (both standalone and through MariaMole But I’m not sure if the PROGMEM section where you build the custom characters is compatible with Arduino 1+ because of depreciated technique or a bug in Arduino… The big show displays the digits 0-7 for the special character demo. I’m not familiar with using PROGMEM myself, but I did some research and tried the various syntax constructs mentioned at With each of my syntax attempts MariaMole casts the following warning “warning: only initialized variables can be placed into program memory area”.

        A minor issue with the big show sketch is in the multi-tap demo (and might just be a change in how NewSoftSerial works from when you wrote the sketch to how it now works as included in Arduino 1+ as SoftwareSerial). The get_text() function uses NSS.print() to send the control characters 14 and 15 which just results in the numbers 14 and 15 being displayed. When I change to NSS.write() the multi-tap demo works as expected. (It would be nice, however, to modify the multi-tap timeout as I found the default a bit fast and the input would change to the next character input before I finished cycling through the multi-tap characters…)

        I think I also noticed a bug that crept into firmware 1.6.2. In the big show’s main menu, I can’t seem to select menu item “0”. I modified the sketch to echo all characters returned from the phi-panel to the hardware serial port and monitored it with the serial monitor. With the shipped firmware and also with phi_panel_20X4_backpack_1_5_1.cpp.hex, when I select menu item 0 to play with changing the back-light level, I saw the expected “0” character echoed. But with phi_panel_backpack_20X4_1_6_2.hex, I didn’t see the “0” character echoed when 0 was pressed. (All the other characters were echoed as expected, and the 0 key works as expected in the Keys and Multi-tap demos. (FWIW, I did upload firmware_erase.hex prior to uploading a new firmware version. And was using v1.00 of Xloader.)

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