Comments on: Hardware

By: fredm

fredm — Tue, 26 Apr 2011 14:36:13 +0000

Nominal battery voltage under load is 9.6v. Diode drop is closer to 0.65v.

By: infiniteloop

infiniteloop — Tue, 26 Apr 2011 14:21:37 +0000

What about when the battery is fully charged? The battery voltage can be more than 10v when fully charged. 10-(.6*5)=7

Am I missing something?

By: fredm

fredm — Tue, 26 Apr 2011 13:56:50 +0000

When there is a load, the voltage will drop; diodes have a characteristic 0.6v drop under load (e.g., 100 mA or more). The circuit actually has a flaw that unloaded, there is no voltage drop. Some servo motors (particularly, the micro sized ones) can get burned out by the overvoltage. Regular sized servos are fine though, and once the servo starts drawing current, you will see the voltage drop to the intended level (5 to 6v).

By: infiniteloop

infiniteloop — Tue, 26 Apr 2011 13:53:03 +0000

As an undergraduate studying Electrical and Computer Engineering, I am interested in how some of the handy board electronics work. I looked at the schematic for the expansion board, but I was unable to understand how the diode chain regulates the servo voltage, especially as the battery voltage varies with charge level.

I also probed the voltage on the servo ports with a voltmeter, and instead of getting 6v, I was getting 10v. This measurement was taken while the expansion board was powering a Futaba S3003.

Can you explain to me how this works?

By: Steve Law

Steve Law — Sun, 06 Mar 2011 18:28:34 +0000

As a follow up to the above post, I did it in software (IC).

By: Steve Law

Steve Law — Tue, 30 Nov 2010 04:23:34 +0000

Hello, I think I just figured out a way to do current sensing of the motors on the Handy Board, and maybe a little elegant too.

I was looking at the MIT 6.720 manual, and it talked about using a connection between the forward indicating LED and the reverse indicating LED to do this with. It gave the schematic on how it is done on the 6.720 board.

This is how it could be done on the Handy Board.
1: Remove resistor pack RP2.
2: Solder a 1K resistor between the 5 volt square pad and the pad right next to the square pad. This is to keep the Start Button usable.
3: Use wire long enough to go from the next four pads to the expansion board and solder a 360 ohm resistor between each of these wires to the + side of the motor power pass through connector on the expansion board J6.
4. Take a tap between the resistor and the wire on each and wire it to an analog input. Use this for your measurement.

Now, with all that said and done, I think I just discovered a problem. What would the maximum output of this circuit be. I didn’t think of that yet. It may be too high for the analog inputs. Have to breadboard it.

Back to the drawing board.

By: fredm

fredm — Sat, 14 Nov 2009 12:58:04 +0000

Yes, you would need to cut traces on both the main HB and the Expansion board. Also, you’d want to separate the servo power source, because servos should not be run on more than 6v. There is a diode chain on the Exp Bd to drop the servo voltage from 9 to 6v, but if you’re putting in 24v, you’d burn out servos. You could remove a diode and use the exposed pad as a place to run a 5v or 6v servo supply.

By: jjohnson

jjohnson — Fri, 13 Nov 2009 21:09:41 +0000

I am trying to use an external power supply to run my DC motors, I found the instructions for using a second power supply for the HandyBoard (http://www.handyboard.com/oldhb/mods/hbmcut.html). I also have an expansion board on my Handy Board, The expansion Board uses these same headers. I also found some documentation on how to modify the expansion board to accept external power for the servo motors (back of expansion board identifies the trace to be cut). If I were to add an external power supply source of 24 volts would I need to cut both of these traces? Would I be correct in assuming that the servo and dc motors would both run on the same external source?

By: fredm

fredm — Sun, 13 Sep 2009 01:43:30 +0000

Jennifer, you can’t use a parallel adapter. You have to get a USB-serial cable, which provides a COM port. You then use a serial DB25-DB9 adapter to connect from the USB-serial cable to the Handy Board serial interface. Interactive C will be able to talk to the board using the USB-serial COM port.

By: jllynch

jllynch — Sun, 13 Sep 2009 00:36:52 +0000

I’m trying to get a handyboard v1.2k to work. I have a 24 pin parallel port (male) that I’m trying to connect to a modern computer. I have a parallel to 9 pin converter hooked to a 9 pin to a usb port on the computer, but the computer will not recognize the device. I’m working with Interactive C v 8.0.2 on a Windows Vista computer. Do you have any advice? In IC the interface keeps asking for a COM port, but none shows up on computer.