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Thread: TEE1010 - A FCB1010 rebuild with a Teensy 4.1

  1. #1

    TEE1010 - A FCB1010 rebuild with a Teensy 4.1

    TEE1010 Part 1 - Testing - A FCB1010 rebuild with a Teensy 4.1

    I'm going to rebuild an FCB1010 into something that is more capable. To do this I am going to gut the internals and install a Teensy 4.1 and Teensy Audio card. I have delusions of it working like a bass pedal, MIDI sequencer and/or drum machine. But.... Will a 5V internal set up work with the 3.3V of the Teensy 4.1. In this short video I tested the Expression Pedals and Switches. I was mostly concerned with the 5V LED setup used for the Expression Pedals.

    I am a guitar player so this foot pedal will be very helpful. Got any good ideas?

  2. #2
    Senior Member Blackaddr's Avatar
    Join Date
    Mar 2017
    Looks like a cool project! I've built lots of custom MIDI controllers and guitar DSP boards over the years. As far as voltages go, yeah, as I'm sure you know 5V is not safe for the Teensy 4.x.

    The Teensy can take 5V in on it's VIN pin so that's nice. But if the FCB1010 circuits are designed to operate at 5V, you need to do some work. Here's my comments (you've likely already figured this stuff out but it might be helpful for readers looking at something similar).

    - LEDs - these circuits likely have an 0/5V signal into an LED and current limit resistor. If you hook this up to a Teensy 3.3V output you will reduce the current and hence the brightness of the LED. However if the stock micro feeds a driver circuit like a BJT, you may not have to do anything at all. Let's assume the 5V micro output directly supplied the current to the LED circuit. You will need to replace the stock resistor with a lower valued one such that when driving by 3.3V, the current is the same as it was when driven by 5V. Instead of desoldering and replacing the old resistor, you can lower the overall resistance by connecting one in parallel with the original such that the parallel combination achieves the desired final value. This is may be easier then desoldering.

    - Switches - You didn't specify in your post but I'm assuming these are pulled up to 5V, and grounded when the switch is pressed. The simple solution would be to disconnect the 5V on to the switch circuit and connect 3.3V from the Teensy instead. However that's probably not the most practical. By adding another resistor in parallel with the switch, you can create a voltage divider with the pullup such that you get 3.3V instead of 5.

    Original circuit: VAL is where the switch state is measured
    5V --- Rp --- SW --- GND
    New Circuit:
    5V --- Rp --- SW --- GND

    - Expression inputs: the FCB1010 circuits are likely designed to go from 0V to 5V (approximately). This needs to be reduced to 0 to 3.3V. This one may be a little harder to correct as expression pedals have very different circuits and the solution must be tailored to that. Attempting to put a resistor in series or parallel with parts of the circuit may reduce the voltage to the correct range but create a non-linear behavior. Since there are very few expression pedals, you may want to simply feed the output of each expression circuit into a BJT voltage follower circuit, then use an appropriate divider on the BJT output to simply reduce the range to the 3.3V target without altering the linearity of the response.

    Much of this based on speculation of the various circuits. If you have a link to a schematic for the FCB1010 it will be easier for people to offer suggestions if you want feedback on your circuit alteration ideas.

  3. #3
    Thanks for your detailed explanations and hints!

    I don't intend to use the 5V of the FCB1010 as I didn't want to have to worry about the Teensy having an input of 5V. I am going to replace the display with an oled that I have used with Teensys before and the MIDI out will need some resistor changes to account for the lower voltage as MIDI is current driven. specifies 10Ohm and 33Ohm instead of 220Ohm
    Other than that the Teensy will be in charge.

    The Expression pedals circuit only draws between 5.66 and 5.84 mA depending on wiper position which is way under the Teensy's maximum of 250mA.

  4. #4
    Expression Pedals: I measured the input to the Teensy vs Pedal Height and got this result.
    Click image for larger version. 

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    The correlation was 0.9975 so everything here is good for 3.3V.

  5. #5
    I want to be able to update and power the Teensy over USB once it is installed. In the past I have just used a USB cable plugged into the Teensy and had it sticking out the side of the case. Not very reliable or neat. I am thinking I need to install a USB socket into the back of the FCB 1010. I intend to use a USB B printer cable type socket because I have plenty of USB printer cable leads spare.


    Does the updating of the Teensys program have to be via the USB input. If I could solder some wires from the board to the USB socket it would be a lot more robust. If not I am assuming the USB connector of the Teensy would best be secured in some way. What do others do?

  6. #6
    Senior Member Blackaddr's Avatar
    Join Date
    Mar 2017
    Well, yes, you have to program the Teensy 4.1 via the USB 'interface'. If you really want to you could attempt to solder wires to the microUSB connector pins pads (they're tiny) and then put a chassis mount USB connector. But honestly, that's likely to be less robust. Just buy a really short microUSB to USB-B Chasis Mount cable off ebay.

  7. #7
    This is a good idea. I bought one, thanks. I am not good enough with soldering to even look those tiny pads.

  8. #8

    Post Part 2 - Choosing the Pin Connections

    In this Video I explain which pins I am using to connect the Teensy 4.1 to other electronics.

    If you don't want to watch the video here are the pins I decided to use:

    Click image for larger version. 

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  9. #9
    TEE1010 Part 3 - Modifying the Insides - A FCB1010 rebuild with a Teensy 4.1

    In this Video I explain how I modified the inside electronics. You can tell by the soldering and general construction that I am more of a programmer!

  10. #10
    TEE1010 Part 4 - Simple Mono Synth Software - A FCB1010 rebuild with a Teensy 4.1

    I'm am rebuilding a FCB1010 into something that is more capable. To do this I have gutted the internals and installed a Teensy 4.1 and Teensy Audio card. I have delusions of it working like a bass pedal, MIDI sequencer and/or drum machine.

    In this Video I explain how I programmed a simple mono synth. So far it has the ability to play in various scales including a major and minor scale. I have also added latch mode and an arpeggiator.

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