I was just asked a great question in response to my YouTube clip of the Time Lord demo: "Will the programmed micro work without the launchpad kit?". I was just going write a quick 'yes' in return since my next project revolves around that ability.
Yet as I hovered over the 'Post' button I realised this was merely an assumption; I had never tested it for myself. So I pulled out some jumper wires and quickly connected the Time Lord chip to a single LED and a battery pack as a quick proof of concept.
I was briefly stumped when the LED remained dark. I double checked all the connections but found no shorts or faults. Using a voltmeter I probed the LaunchPad board's DIP socket and quickly discovered my problem, the RST pin on the LaunchPad was being supplied with current!
I did some Googling and confirmed the microcontroller is held in the reset state while the RST pin is low. After adding a wire between RST and the postive battery terminal the LED came to life as expected.
The final jumper wire connections were as follows:
Red - Positive battery terminal to MSP pin 1
White - MSP pin 2 to LED anode
Green - LED cathode to negative battery terminal
Yellow - Positive battery terminal to MSP pin 10
Black - MSP pin 14 to negative battery terminal
Pretty Cool... Why not breadboard the microcontroller and connect with two pushbuttons and LED just like your Time Lord game?
ReplyDeleteSorry for all the comments :-P
ReplyDeleteGareth, it would be a good idea to hook up the RST pin with a resistor to the positive battery terminal. There are multiple reasons for this, but I won't go into it here. It is also a good idea to use a low value resistor in series with the LED to limit the current draw.
I'm jealous of all your cables :-P very cool.
Tabish,
ReplyDeleteSadly I don't have a breadboard yet otherwise I would have (I only got around to ordering one last week).
NJC,
Do you know what the minimum voltage would be to keep the RST pin happy? I don't recall seeing it in the datasheet but I am new to reading them. I am now using a 150R inline with LEDs to limit them to 20mA on a 3v supply and all is good.
All tips are greatly appreciated, everybody!
So what is your next project Gareth?
ReplyDeleteI'll have a post up tomorrow about it, Tabish :o)
ReplyDeleteIt's going to be a multi-post project on account of the fact I suck at circuit board layout - I just built my first ever board yesterday! It's fairly small and basic but still took me most of the day :o(
I planning a sort of enclosure too. Hopefully it'll be a bit of a progression from the jumble of wires in the video above.
Nice hack. I'll blog about this in a few minutes. You could even use a coin cell to power it up. Make an LED throwie!
ReplyDeleteHello. If u do get this comment, make sure in the future, to connect the reset pin HIGH by a pull up resistor (47K ohm) connected directly to the V+ of the power supply and make sure that the Vcc pin is decoupled by a 0.1uF capacitor---> helps to give a clean AC free DC voltage to the uC
ReplyDeletehttp://dangerousprototypes.com/docs/MSP430_quick_start
This might help!!!. Happy coding
Thanks for the tips, Anon.
ReplyDeleteI've never found an explanation for the pull-up resistor on the reset pin. The circuit has been working perfectly for ages without it. I guess it is just to reduce power drain through this pin?
Also while the cap would be pretty crucial for a circuit powered by an AC-DC converter surely a simply battery will provide a clean enough supply that this filter is not required?
I'd be interested to read your thoughts.