cmatthews
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Gertduino & TinkerKit SensorShield

Mon Dec 23, 2013 11:19 pm

I have been working with an Arduino TinkerKit SensorShield and the Gertduino.

It works, but programming the Gertduino with the TinkerKit shield in place doesn't work. The workaround I arrived at was to upload the sketch to the Gertduino, power down the Raspberry Pi, fit the TinkerKit shield and then power back up. I am assuming that this is a power issue because on the official Arduino Motor Shield, I get a similar situation but can work around it by powering the motor drive from a battery or external supply. Is this is a bad assumption or is the TinkerKit shield interfering with the IO used to BitBang the ATmega328p?

IF it is a PSU issue, how bad an idea would it be for me to connect the 5v supply pin to an external supply? I understand that the 5v supply on the Gertduino was not fitted because of worries about the heating effects of back-feeding (http://www.raspberrypi.org/phpBB3/viewt ... 1&p=467751).
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Gert van Loo
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Re: Gertduino & TinkerKit SensorShield

Tue Dec 24, 2013 11:22 am

I don't know the Tinkerkit but the cause might be the level converter resistors between the pi and the Gertduino.
I use resistive dividers in case somebody uses one of the programming pins as output.
This way the 5V of the Atmega does not end up on the 3V3 pins of the raspberry-Pi.
This means that between the Pi and the Gertduino is a series resistor of 3300 ohm.
If there is a load on the other side (e.g. some electronics with a low impedance) the programming won't work.

Yes, I could have choose a much lower value but then the 'other' resistor had to be lower as well which means
a high permanent load on the GPIO pin and the Atmega pin.
In the end it was a balance between resistive values, load, drive strength, system complexity & cost.
(Cost is very important as a user which spends $35 on a PI is unlikely to spend much on a Gertduino.)

I am assuming that this is a power issue because on the official Arduino Motor Shield, I get a similar situation but can work around it by powering the motor drive from a battery or external supply.
It is a power issue but not directly. When the P3 shield is not powered the control inputs are very low impedance and then you get exactly the problem I explained above. When there is power on the P3 motor shield the inputs become very high impedance and the problem goes away.

If you can point me to a schematic of the Tinkerkit I can have a look.

cmatthews
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Joined: Fri May 11, 2012 9:05 pm
Location: Wirral, UK

Re: Gertduino & TinkerKit SensorShield

Sat Dec 28, 2013 4:08 pm

Gert,

Thanks for your reply. I haven't been able to find a Schematic for the TinkerKit. I will see if I can get one.

Christian
www.mydominion.co.uk

vf171ohio
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Re: Gertduino & TinkerKit SensorShield

Thu Aug 07, 2014 2:49 am

Do any sensor shields work the Gertduino? I'd like to get my daughter something that makes it relatively simple to work with sensors and not require constant assembly/disassembly if at all possible.

cmatthews
Posts: 84
Joined: Fri May 11, 2012 9:05 pm
Location: Wirral, UK

Re: Gertduino & TinkerKit SensorShield

Thu Aug 07, 2014 7:27 am

The sensorshield works OK, it is just necessary to program the Gertduino without the shield in place. I never did get to the bottom of why this was the case. The Tinkerkit + Gertboard combination still offers a nice platform in terms of flexibility and ease of use, even with the slight inconvenience w.r.t. programming.
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hansotten
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Re: Gertduino & TinkerKit SensorShield

Thu Aug 07, 2014 7:56 am

cmatthews wrote:The sensorshield works OK, it is just necessary to program the Gertduino without the shield in place. I never did get to the bottom of why this was the case. The Tinkerkit + Gertboard combination still offers a nice platform in terms of flexibility and ease of use, even with the slight inconvenience w.r.t. programming.
I assume this is the Tinkerkit: http://store.arduino.cc/product/T020010

As far as I can see such it is just a passive device itself.

So it may be your programming problems come from sensors attached.
What do you have connected? Serial? Unplugging during programming may reveal the source.
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