HomeWork board
J. A. Streich
Posts: 158
3 quick questions about the BS2 HomeWork board...
1.) The serial conection is it male or female? Does it use a null modem or a cable that has one male and one female?
2) Does it ship with a cable? (I've been assuming that it does not, and I'll have to buy them seperatly)
3) It only has a 9 volt power, and not a barrel for a AA battry holder. So, if I want it to drive parallax continuouse rotation servos...
A.) Can I just make one output pin high (as it regulated), one for the serial input and the other tied to vdd? Or would the current kill the servo?
B.) If I can't do A, what would I have to do step down the power?
Many thanks in advance.
1.) The serial conection is it male or female? Does it use a null modem or a cable that has one male and one female?
2) Does it ship with a cable? (I've been assuming that it does not, and I'll have to buy them seperatly)
3) It only has a 9 volt power, and not a barrel for a AA battry holder. So, if I want it to drive parallax continuouse rotation servos...
A.) Can I just make one output pin high (as it regulated), one for the serial input and the other tied to vdd? Or would the current kill the servo?
B.) If I can't do A, what would I have to do step down the power?
Many thanks in advance.
Comments
(1) DB-9 on the HomeWork Board is F, which is connected to your serial port with a straight-through serial cable (no null modem or other funny stuff).
(2) Yes, in the RadioShack "What's A Microcontroller Kit". Parallax only sells them in 10-packs on our web site, but if you really only want the board alone then call our sales staff and they can sell you a HomeWork Board alone.
(3) Correct. You can get a 9V clip to two-wire connector at RadioShack. You can attach the two wires to a 6V power supply for your robots. Then, the servos can be connected to Vin (in fact, they can also be connected to Vin with a 9V battery and it will work fine, but it's a bit beyond the servo spec of 7.5V).
(3A) Sure, but I'm not sure what you want to accomplish by doing this. All pins can be used anyway you want them. If you are controlling servos then they won't have a serial interface for control, but a pulse signal between 1 and 2 ms. In general you aren't going to kill the servos with any 6V power supply. But you could damage the BASIC Stamp by using its regulated Vdd to power the servos (this is why we suggest using the Vin connection for servos on top of the breadboard).
(3B) I think I answered that above.
Basically, it sounds like you want to use the HomeWork Board in lieu of a BOE for your robot. This is perfectly acceptable. All you're really missing is the convenient servo header conenctors, the AppMod connector (not too important), a slide switch and a larger regulator. Much of our staff prefers the bare approach of the HomeWork Board because there's no extra hardware laying around for projects where it is not required.
Does that help?
Ken Gracey
Parallax, Inc.
That's what I thought. I found a deal on Null modem cables, but the straight through serial cables are a bit more. I'll cope.
> (2) Yes, in the RadioShack "What's A Microcontroller Kit". Parallax only sells them in 10-packs on our web site,
> but if you really only want the board alone then call our sales staff and they can sell you a HomeWork Board alone.
I've contacted sales previously, I'm actually putting together kits (about 30 or so), as an educational/fundraising event for our university's chapter of IEEE-CS.
> (3) Correct. You can get a 9V clip to two-wire connector at RadioShack. You can attach the two wires to a 6V power supply for your robots.
> Then, the servos can be connected to Vin (in fact, they can also be connected to Vin with a 9V battery and it will work fine, but it's a bit beyond the servo spec of 7.5V).
There was a warning in the BOE text about using 9v and vin to drive servos, so I thought that using the voltage after it's been regulated down to 5v was "safer", but if you think that Furbuta servos can take it... Then I don't need to tie up the extra pins.
> Basically, it sounds like you want to use the HomeWork Board in lieu of a BOE for your robot. This is perfectly acceptable. All you're really missing is the convenient servo header
> conenctors, the AppMod connector (not too important), a slide switch and a larger regulator.
Exsactly what I'm doing. I was going to use 3 pin header on the bread board to drive the servos. The app mod connector can be made on the bread board, too (though it would take up more realestate than I'd like). The slide switch for reset I can live without, and if the 9v can drive the servos I can live without regulator.
> Much of our staff prefers the bare approach of the HomeWork Board because there's no extra hardware laying around for projects where it is not required.
The HomeWork board is also a lot cheaper in bulk, which is why I opted to take this route. The only thing left are non-electrical hardware (read: screws, standoffs and chassis (we have a canidate, but I'm not satisfied with it). Any suggestions on chassis and screws would appreciated.
> Does that help?
Yes, very much so. Now, I'm off to look screws.
DB-9 cables are cheap. Retailers like Fry's, Best Buy and RadioShack charge you a body organ for these things. And those fancy Belkin ones are no different than our Taiwanese cheapie. Don't pay more than ten bucks. In fact, if you have an electronics surplus supplier they might even be three bucks.
Okay, the servo voltage is a matter of some disagreement even within Parallax. I think the reference you read in the BOE docs are in regards to 9V from a wal-wart supply. Even our 9V wal-wart puts 10-14 V without load and it has poor regulation. That's why the BOE has the Vin/Vdd jumper on the servo header block. But with a 9V battery on the HWB you'll measure 9V and maybe less once you're applying a load. The servo will turn more quickly with a 9V supply than a 5-6V supply, too. You'll shorten the servo life with 9V and the case will get hotter, but I've never seen smoke from 9V. And I love to break stuff. In fact, our entire What's a Microcontroller? Kit sold through RadioShack includes a standard servo. It is powered from Vin (9V battery) on the HWB.
And servos are cheap. Also, we have 30,000 of them in stock (please buy some of these). This is good for you, because you get to buy them at our cost! The Parallax continuous rotation servo is a Futaba S-148, and our price should be lower than anywhere in the western hemisphere.
To minimize the HWB real estate requirements for the servos, you can get it down to four breadboard rows. Overlap Vss and Vin, and put the two signal connections on the outside.
For the screws, standoffs and chassis, we can sell you those parts in bulk. My suggestion is to contact Jim Carey, my sales manager (jcarey@parallax.com). You are probably already working with him, Paul, Kristina or Chantal (this team really rocks - they're our stars!). We often sell the raw materials to customers who need more than a few dozen. This wouldn't be done through our web site, normally. To make this part easy for our sales staff, visit the Robotics with the Boe-Bot text and pick out the Parallax part numbers you need for "everything below the BOE" and ask for a quote. There's a Boe-Bot Bill of Materials in the appendix of that book.
Sounds like you've got everything in order.
Sincerely,
Ken Gracey
Parallax, Inc.
As far as the servos, if you are going to offer any type of documentation with your kits you might suggest ramping when sending servo positions, that may help extend the life that may otherwise be lost due to the use of 9v. (Maybe, maybe not...)
You might consider just using the 9v for the BS2 power, and an AA combination for the servo power- you could use the zip-tie holes for mounting that UNDER the board...just a thought ...
Ryan
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Ryan Clarke
Parallax Tech Support
RClarke@Parallax.com
> cheapie. Don't pay more than ten bucks. In fact, if you have an electronics surplus supplier they might even be three bucks.
I was looking at a $6.00 cable from Jameco, a Null Modem Serial Cable, then I looked over at my BOE cable and realized there might be a problem... Hence the initial post. The result is a $2.00 straight through I found a minute ago.
In regards to the Servo, one complaint I've seen from people who might be buying our kit is that the servos on my personal BOE aren't "fast enough," Running the 9v will be a little faster, and I suspect that some people will swap them for stepper motors fairly quickly. So, I'm not worried about the servos running hot.
> And servos are cheap. Also, we have 30,000 of them in stock (please buy some of these). This is good for you, because you get to buy them at our cost!
> The Parallax continuous rotation servo is a Futaba S-148, and our price should be lower than anywhere in the western hemisphere.
Yes, I spent a long time looking at motors, and yours are the lowest I've seen anywhere. Very impressed.
> To minimize the HWB real estate requirements for the servos, you can get it down to four breadboard rows. Overlap Vss and Vin, and put the two signal connections on the outside.
That will require the wire comming out of one of the servo to be cut, and re-arranged... Happen to know if they are they standed or if they are solid?
> For the screws, standoffs and chassis, we can sell you those parts in bulk. My suggestion is to contact Jim Carey, my sales manager (jcarey@parallax.com). You are probably already
> working with him, Paul, Kristina or Chantal (this team really rocks - they're our stars!).
I've been working a little bit with Paul... Seeing what he could do with price breaks on BOE-Bot. I'm way under the bulk price for the serial BOE-Bot, but I'm looking at using a VERY cheap chassis (a floppy drive mount for mounting the 3 1/4 into the fullsize bay) -- I'm not happy with the idea (hence the search for chassis substitutes).
Basically, if I use the floppy, I'll need:
- 8 screws with nuts or washers for the servos
- the 4 stand offs
- 4 small screws to screw into the standoff
- 2 screws for the LCDs (weren't in the original plan, but I saw a post about cheap LCDs in the sandbox) -- should fit in the opening of the drive (may require a little drilling/cutting)
? Not sure about how to support the back end... ?
If we go with a Boe Chassis:
- Drag wheel
- Pin for the Drag wheel
- Chassis it's self
- 8 screws with nuts or washers for the servos
- the 4 stand offs
- 4 small screws to screw into the standoff
? Not sure I know the best way to mount the LCD on BOE -- I'll be reading the Parallax LCD manual, and it should have a few ways... ?
Missing anything "metal shop" related?
> We often sell the raw materials to customers who need more than a few dozen. This wouldn't be done through our web site, normally.
> To make this part easy for our sales staff, visit the Robotics with the Boe-Bot text and pick out the Parallax part numbers you need for "everything below the BOE"
> and ask for a quote. There's a Boe-Bot Bill of Materials in the appendix of that book.
I shall do just that.
> Sounds like you've got everything in order.
Trying to... Almost there.
> I wouldn't suggest trying to build up the AppMod header on the board, rather just connect up what is needed at the time.
Well, the initial kit won't have AppMod header, but if there is enough intrest (and I suspect there is) I plan to do a second event (with 2 sections or sessions) where we'll sell our base kit to people who didn't get them the first time, and AppMods for people who got the kit at the first event.
> As far as the servos, if you are going to offer any type of documentation with your kits you might suggest ramping when sending servo positions,
> that may help extend the life that may otherwise be lost due to the use of 9v. (Maybe, maybe not...)
The documentation is being written, which is when I noticed the warning in the BOE text. At the moment it's just a basic run down of the PBASIC IDE for windows. It will grow to include how to use the Linux tokenizer program (as we're a computer society, and host Linux Installs), over the weekend. The assembly portion will be written when we assemble our first kit (it'll be used for demo and display), and we can take pictures at each step for the manual.
Microprocessor and control board:
Parallax HomeWork Board
http://www.parallax.com/detail.asp?product_id=28158
avabile in packs of 10.
Price per bot: $40
Price per order (of 30): $1,125
Servo Motors (on sale):
Parallax (Futaba) Continuous Rotation Servo
http://www.parallax.com/detail.asp?product_id=900-00008
$6.95 each, 2 per bot.
Price per bot: $13.90
Price per order (3 of 10 each): $417.00
IR Emiter Diode (read: IR LED for wall detection)
http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=112150&pa=112150PS
Price per bot: $0.28
Price per order (of 100): $14.00
IR Detector
http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=112176&pa=112176PS
Price per bot: $0.38
Price per order (of 100): $19.00
LEDs
http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=135271
Price per bot: > $0.10
Price per order(1 bag of 1900PCS): $44.95
Chassis -- Not set on it... Other ideas???
http://svc.com/cm-525-35-sv-19.html
Floppy chassis is cheap price wise, but also looks cheap.
Price per bot: $2.99
Price per order (for 30): $80.70
LCD screen
http://www.allelectronics.com/cgi-bin/category.cgi?category=365&item=LCD-107&type=store
I found a very reasonable LCD screen
Price per bot: $4.00
Price per order (for 30): $120
And, I have an idea for wheels...
http://www.skate-buys.com/skatebuys/bauerhocinsk.html
$3.49
Price per bot: $6.98
Price per order (for 60): $209.40
DB9 Male / DB9 Female, 9C, Serial Cable, Molded, 1:1, 6 ft
http://www.sfcable.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=db9&source=google
Price per bot: $2.00
Price per order: $60.00
Headers, need to connect the servos to something.
http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=53495
10 headers -- 26 pins each -- each person needs 2 sets of 3 pins
Price per bot: > $0.29
Price per order: $29.00
Let me take a look at the list. . . okay I'm back with a reply.
HomeWork Board => OK. No problems here.
Continuous Rotation Servos. => OK. You need tires (rubber bands and wheels?).
IR Emitter from Jameco => OK. See no problems. You will need to device some kind of shield around the LED (such as our shield, if they fit) or use something like a bit of electrical tape to focus the beam.
IR Detector from Jameco => Not sure about this part - it's a phototransistor. May work for simple IR detection but will need more opinion on this discussion forum about using it on a robot. We use this in a short-range IR application in our Process Control text, but it's not tuned to 38 KHz like the receiver we sell.
LEDs from Jameco => No problem.
Chassis from SVC => No picture displayed when I looked. Looks like this is a floppy drive bay and it costs $2.99. What's preventing you from using the Boe-Bot chassis? Cost?
LCD screen from All Electronics => Looks like Hitachi HD77480 compatible. Should be okay. Buy one before you buy 30 units. Test it with code from StampWorks.
Wheels => About the same price as Parallax wheels. Considering the difficulty in mounting these to a servo horn I'd prefer just to use Parallax wheels if I were your student (unless fabrication is part of the whole robot project, then it's fine to drill holes.
Serial Cable => OK, seems fine.
Headers from Jameco => Should be fine - watch out for flying parts when you cut them.
What's the total unit cost per kit?
Ken Gracey
Parallax, Inc.
HomeWork Board => OK. No problems here.
Continuous Rotation Servos. => OK. You need tires (rubber bands and wheels?).
Those are later in the list (and you talk about them...
IR Emitter from Jameco => OK. See no problems. You will need to device some kind of shield around the LED (such as our shield, if they fit) or use something like a bit of electrical tape to focus the beam.
I was thinking of using electrical tape, but I'll check sizes against the Jameco LEDs.
IR Detector from Jameco => Not sure about this part - it's a phototransistor. May work for simple IR detection but will need more opinion on this discussion forum about using it on a robot. We use this in a short-range IR application in our Process Control text, but it's not tuned to 38 KHz like the receiver we sell.
I was/am worried about it... I think I may keep it simple and go with the detector that is in the BOE-Bot kit ( http://www.parallax.com/detail.asp?product_id=350-00014 ).
LEDs from Jameco => No problem.
The grab bag seemed the way to go... A little bit of everything.
Chassis from SVC => No picture displayed when I looked. Looks like this is a floppy drive bay and it costs $2.99. What's preventing you from using the Boe-Bot chassis? Cost?
When I first veiwed it there was a picture. Cost was the issue. BOE's chassis is pretty darn useful, and I think better looking; but, I was over ruled on it. The reason we went looking at drive mounts was because "we just need a peice of metal, right?" I realize that this will require heavy use of dremmel, and personally, I'm still looking for a better option. Parallax Sales can't give me enough of a price break to convince the other guys it's worth the cost for a bot chassis. One of the guys is hung up on errrector set stuff, but it's expensive and too specaillized. Any advice here would be appreciated.
LCD screen from All Electronics => Looks like Hitachi HD77480 compatible. Should be okay. Buy one before you buy 30 units. Test it with code from StampWorks.
The LCD wasn't originally in the plans, untill I saw a post about it in the sandbox... Apparently it operates with the same control signals as one of the Parallax LCDs, so there is a white sheet that we can use for using it with the BS2. Although, I think your right about buying a test unit first.
Wheels => About the same price as Parallax wheels. Considering the difficulty in mounting these to a servo horn I'd prefer just to use Parallax wheels if I were your student (unless fabrication is part of the whole robot project, then it's fine to drill holes.
What I was thinking is to mount it through a servo horn, by putting screws straight through the spaces between the spokes.
Serial Cable => OK, seems fine.
It's a cheapy...
Headers from Jameco => Should be fine - watch out for flying parts when you cut them.
I've never
What's the total unit cost per kit?
I did all the summing as I was hunting, if I didn't miss anything, it should be (our costs):
70.82 (this includes some rounding up on items in bulk) per bot
1840.40 for 30.
excluding screws and standoffs, which I still need to look into.
On the wheels... BOE's original wheels (white disks) are a bit to unstable (I have a BOE that likes to stray to one side, if I don't correct the problem in the code). The other BOE-Wheels are nice, but priced a bit high... The skatewheels are durable and take a beating... The only concern is weight, and rigging it to a servo horn. If this proves to difficult, the black BOR-Bot wheels will be the way to go. I think I'll have to print a mock-up (or go to a local skate shop and buy one) and see how they line up and what kind of screw I'll need to hold it. Any other wheel ideas are still open.
I'll be getting the okay to use the funds on the 8th, and on the 10th I'll be placing orders.
Wheels: I thought about using balsa wood... But they would suffer from warping and the wobble would be worse than the white Boe wheels, but I might be able to cut a dowl to the right size. I also gave thought to wooden craft wheels from a craft shop. I forgot why I ruled out the craft wheels... hmmm...
Note on over lapping: I finally realized what you were saying about over lapping... The IR Detector (Parallax) has three leads, the IR led will need power and the servo will need vss and vdd... True for both sides. I am thinking something like the attached... The I/O pins of each aren't connected to I/O pins in my diagram to save space for more drawing, but the basic idea is there. The hairpins in front are the LEDs (lengths of legs in my drawing don't show direction of diode), second row is the IR Detecotor, and the third is the servos (black to green (Vdd), red to red (Vss), and white to I/O pin).