Parts are here! Parts are here!!
Just got home from work and there was a big, sexy digi-key package waiting!!!
Just gotta finish my PCB layout and start etching!!!
–Check out those sexy-sexy anti-static bags, yo!!!
gonna get mine soon too!gonna get mine soon too!
**A question for robologist. **
A question for robologist. Could you skip the TC4427 driver if you used 2 IRLZ44N FETs . The (L) designation being Logic driven (5v) ? in the "BOA’s Brilliant Hybrid H Bridge - Robologist Mod’design?
To PWM or not
The logic level FETs can be switched by a 5 or 3 volt signal, but even these FETs will switch "better" when slammed on or off with a driver voltage. I like setting PWM up at 20 kHz or so, to get it out of hearing. You can get different responses from motors with varying frequencies, but to really ensure quick turn on / turn off of the FETs, there is a significant difference between a MCU pin sending a max of 10 mA to charge the input capacitance of a FET gate, and a driver hitting that same pin with 1.5 A to charge it up.
Pull down resistors???
I am just finishing the layout for my board and thought it might be a good idea to add some pull-down resistors on the inputs going to the 2 transistors that are switching the relays. --Any reason to?
I don’t see any reason
I don’t see any reason too. BJTs like the NPN 2N2222 require current to flow through the base in order for the switch to be on. Even if there is a minute amount of unwanted current on the inputs, it will flow through the base probably before flowing through the resistor. I assume the input will be coming off the PICAXE. I would suggest to put 1 K resistors on the inputs from the PICAXE. These are called biasing resistors and they restrict the amount of current being pulled from the PICAXE.
In some cases it might prevent the PICAXE circuitry from burning up, if its over-sourced, unless they already have resistors on their digital outputs.
Does this make sense or did I mangle it like a frog blender smoothie?
Wicked good, GroG!
Fantastic info, my friend!
I am soo stoked with this PCB layout -Perfect!- I love any ideas about Picaxe protection, yo. --And I can dig what you are layin’ down ‘bout the pull-down’s and will be kickin’ it wit da 1k’s… Oh, yeah…
Yo, check dis… I all be up on da etchin’ and shiiit in da nex couple days and ■■■■■ yo! – ‘All be up and bustin’ dat… Word…
Yeah, all up on the etchin’ style…
**Oh yes, indeed… **
Oh yes, I do indeed intend to represent!
Where we are now (pics and a new post soon)
The PCB Layout is DONE!! I am heading to Staples tonight to get it copied -My printer is ink, not toner.
I should be etching tonight!
As I said above, I am going to document everything but I will start a new post on the subject and linkify back to this thread. It seems no one will ever find the info burried in 45 replies. --I am so stoked!!!
preaching to the choir
blog it! blog it real good!
haleluya ! praise the Asimov
Issac Asimov ain’t got nuthin’ on my etchin’
Well, here it is!
Ok, this is just a mock-up and I know some of the componants are in backwards -all will be double checked before I do final soldering. I just did this quick mock-up to be sure everything fits. Also, my wife is on holiday in NY now and has the digital camera... This pic is from my mobile so I appologize for the quality.
So far, so good -I am happy with the layout and it seems I did the layout on the back correctly. When I solder it I plan to beef-up the little jumper wires. Also, I am a little ify about the LED's. I had some extra room on the board and decided to add them. The 2 greens blink (well, should go bright and dim) with the PWM signal comming in and the red's indicate the reverse signal is on.
Again, I will do a proper post including all the pics I took of the etching process etc. as well as a link to the board layout and schematic. Soon!
You are soooo gonna get busted!
You are toast Chris! You will get BOAsted!
BTW, how is your FeCl supply lately?
wink wink
Yeah, I know…
I know, I know, do it like BOA with just the outlines etched… But really, this is just the least of my worries, I have the oppertunity to solder 18 componants in backward!
Oh, don’t you worry.
When that happens, we will scold you about that as well. To no end!
Board is DONE!!
Ok guys, here it is… Ready to be plugged in…
First test coming up... I am looking forward to what 12v blue smoke looks like! --And off of a car battery no less.
Thanks again for all your help, folks. If I got everything right, as I said before, I will do a proper post of everything.
Christ, this is scary...
oooohhhhbligatory comment
Oooohhhh, aaahhhh, whoahahhh.
And some genuine stuff for desert:
Would it be possible to detect really big errors early on, avoiding smoke emitting diodes (SED) by powering it with, say, 5 V? Measuring battery current while it’s “running”.
8ik
Measure inputs
Are you sure you have 0V at the input? Can you measure it? How come you have 1.6 AND 2.3? Is that different readings for each output?
I can explain the current reversing when you click the relays… Do I need to?
my test set up
First, yeah I got the reversing idea -I just added that so you guys could better diagnose where in the circut this could be happening.
Here we go, I have 12.06V from a computer power supply going into the input. To trigger the driver and relay transistors, I am using a 3 AA battery pack -The ground is tied to the 12V ground and the + lead I am simply touching to each of the data inputs. I am using a meter on the output. As for the 1.6 and 2.3, I have gotten different readings at different times and variances from each output. Generally, it is about 2V or so.
Well grounded
Seems pretty strange, but I’d guess that whatever is providing the switching may not be sharing a ground with the h-bridge board. Maybe. It would seem there could not be any switching if there weren’t a shared ground to start with though. I guess you could try a pull down on the input of the TC4427, to see if it works. Trying to see if anything else in the circuit could be trying to pull anything up. Are the FETs getting warm? Oh, just thought, is there a 0- volt input to the FET driver, or is it just disconnected? An actual 0 v ground signal is needed, floating inputs can do many things. Maybe a pull down on those inputs could be a safety measure if the driving micro fails.