The Lounge

[Jon Chandler]

the stack of TAP-28 boards is growing small, so I'm putting the finishing touches on revision A. I have connected the errors requiring a couple jumpers and made some other improvements, driven largely by the "I wish..." and "Why didn't I..." thoughts I had while using the TAP-28 for various applications.

TAP-28 rev A.jpg (53.45 KiB) Viewed 617 times

The changes include

• Board length increased by 0.25" to 2" x 3.5"
• Resistor patterns lengthened to allow resistors to lay flat
• Clearance around daughterboard connectors increased
• USB Connector (for power only) changed to a mini-B
• Separate terminal block location for power input
• 3-Pin connectors rotated, with patterns for keyed connector
• Pads added near 3-pin connectors to allow addition of pull-up or pull-down resistors
• S1 and S2 pads allow vertical or right-angle switches
• LED pads allow vertical or right-angle LEDS to be used
• Solder jumper pads re-arranged
• Access to ends of PIC location improved for removing PIC from socket

Electrical Changes

• Portpin A2 routed to ICSP connector, pin 6.
• Portpin A3 routed to LED4. It had shared B2 with UART connector pin 6.
• Solder jumper added for the UART power connection

I think most of these changes are self-explanatory. Changing the switch and LED patterns allows right-angle parts for accessible controls in an enclosure like I used for the signal Generator. Adding the patterns for pullup/pulldown resistors to the 3-pin connector locations allows for applications like a Dallas OneWire sensor pullup resistor. If a UART-USB adapter is used, the option to disconnect its power connection is handy if power is supplied by another source.

The mini-USB connector is surface mount with through-hole mounting ears. The mounting ears keep it in place and the solder pads are large, so it should not be too difficult to solder. The the exception of this connector and optionally the switches and LEDs, the parts list is the same as for the original board. The daughterboard connector spacing is unchanged.

Any comments are greatly appreciated. I hope others will find this board as useful as I do.

Jon

[Graham Mitchell]

Nice Jon, it's moving forward well

I did notice a couple of silkscreen bug-bears, it's just cosmetic stuff, though you did ask for comments

silkscreen stuff.png (236.13 KiB) Viewed 609 times

Yellow - overlapping ">E$" labels
Blue - tight fit of those components. It also overlaps with some silkscreen
Purple - another silkscreen overlap (or is it really close? Not sure?)

There are several components that have no ID - Easily solved with the aid of a picture if need be

Are the daughter-board pinout dimensions the same as the original?

[MrDEB]

Am curious why you didn't just use the 40 pin version of the 18F2420?(assuming basically the same as the 18F242?)
would it not of had more pins available?
Working on my 18-40 board and just looking at pic pin-outs.
Using the Tap-28 as an example of what to include. I really like this bare bones development board idea. Looked at the development board from Sure as well as others (read over the artical I believe Jon posted) Great insight into PIC developement boards.

[Jon Chandler]

Thanks for the comments Graham. Yes, there's a little cleanup on the silkscreen. The E$ labels won't be there.

Regarding the pads to the right of each 3-pin connector...this is where a pullup or pulldown resistor can be added to these connectors. The pattern is on the large side for what's there...it's a vertically mounted resistor, one leg to the port pin and the other leg to either V+ or ground. Given that no clearance is needed on the back side of the connector, I think there's enough room there. I don't really like the vertical resistor arrangement, but there's not enough space to allow for 2 possibilities otherwise.

Good call on the label in purple. I can probably shift the solder jumper pads or resistors to spread things out a bit.


Jon

[Jon Chandler]

MrDEB,

My design parameters are for the cheapest possible configuration to fill the largest number of applications. The TAP-28 meets many needs with functions logically laid out on the connectors.

There probably is a need for a 40 pin board. But the board would need to be larger and more connections needed for the port pins. The 6 pin connectors make sense on the TAP-28 and they are for the most part interchangeable - power, ground and 4 port pins. If I don't need the UART or I2C/SPI, these connections are functionally equal. A keypad/LED user interface designed to plug into one connector can use the other with minor changes in the code. The use of dedicated connectors is a key point in the TAP-28. A header connector with all the port pins brought out (just like every other dev board) doesn't lend itself to embedded applications.

One possibility I have considered for a 40 pin part would be similar to the TAP-28 with a dedicated connector for an LCD display. This would handle a lot of applications.

[MrDEB]

good point on the 6 conductor connections.
I am presently drawing up a schematic using your Tap-28 as an example, combining some of the features of the Sure Electronics board, mainly the push-buttons using caps and pull-up resistors. Purchased several double row headers from Sure hoping to use jumpers instead of solder jumpers. I realize the Tap-28 is a bare bones design, I am just trying to make it easier to get up and running.
A big issue I am having is using the Junebug and the USART. Planing on a DPDT switch and use the ICSP port for the USART.
Will post schematic after I clean it up a bit.
Is there an easier way to post a schematic without posting on say photobucket then linking to the picture of schematic. Your tutorials are great without any outside links.
Have a header for an LCD daughter board along with an LCD daughter board.

[Graham Mitchell]

Is there an easier way to post a schematic without posting on say photobucket then linking to the picture of schematic

When making a post click on "Upload Attachment" (at the bottom of the editor window) and find your image.

Note - you need to have the 'Full Editor' open for that option, not the 'Quick Reply' editor

[MrDEB]

will give it a try later.
Thanks

[DomS]

the F2550 is a very nice processor for USB, self powered projects.

I do like the mini-B USB change, as I have tons of those cables here doing nothing.
Do you have space on the board to make the data pins available? Even if it's just a header 10mm away.
Surface mount is scary :Z ... to me

[Jon Chandler]

Sadly, the other functions on the 18F2550 are different than for the other 28 pin parts. It messes up the UART or I2C/SPI mapping and a cap is needed on the Vusb pin which is a Port C pin otherwise.

I like the USB parts too and I use one in another application. If there is some interest, I'll do a TAP-28 USB version as well. I would remap the pins to maintain functional compatibility to the TAP-28 (e.g., Rx and Tx would be on the UART connector, although they might be different port pins).


Jon