[The subject of this post includes a reference/homage to a regular feature in the ARRL's QST magazine. As a kid I had a large box full of old QSTs and spent many hours reading them.]
Designers of small boards often struggle with layout of the pins for headers. The limited real estate makes breaking out enough pins that are sill breadboard friendly very difficult. The Digispark (with USB port) is no exception.
The six pins along the edge are perfectly happy in a breadboard. However, the three others that wouldn't fit on the edge¹—5V, GND, and VIN are at right angles to them, and as you know on a breadboard the pins all have to run one way. If they don't, you can choose what to short out but something is going to be shorted. The usual thing is to choose what you want more in the breadboard and omit the header from the others, or install it topside. A right angle header is sometimes very helpful for that.
However, by a happy coincidence, the case of the Digispark provides and opportunity for a little hack, Its layout happens to almost match the holes in the board and the rails, which are common at 90° to the main board busses.
The fuscia lines indicate the common connections, the dashed line is the hole centers on the main board.
So we have the main busses at 90° to the rails, so that's good but as you can see from the dashed red line, the holes on the rails are, for some good reason one hopes, offset by about .05". The Digispark's pins are apparently laid out on an imaginary .1" grade over the entire board so that places the pins .05" out of alignment with the otherwise fortuitous fact that the rails are just in the right spot to match up with the 5V and GND pins.
If you solder the pins in properly and do a good job, the board just isn't going to fit. So what to do? Some people use a trick to solder headers that involves putting them in a breadboard as a sort of vise and soldering in place. I don't really like that method on two counts:
1. There is a real possibility of overheating and melting the breadboard, and while I have no proof of it, the not-so-robust construction of most breadboards leads me to suspect that even in the absence of a melty outcome the reliability of the heated holes in the board could be diminished.
2. I have found it is possible to have the pins at an angle and not know it until you attempt to extract the completed job from the board, only to find the pins are holding it in like staples. This is no fun to fix after you've managed to free it, particularly on boards with 10s of pins on each side.
But, it is that second bit that plays to our advantage in this case. The lesson learned from the "trick" is first of all, if you are going to do it, just tack in the end pins on each header, then finish out of the breadboard, and if for some reason you want angled pins, you can get them.
The tips of the pins are in the holes they will be pushed into, note the empirically achieved perfect angle.
As you can see in the photo, the pins for the rails are angled based on the actual insertion of the board. The photo is post-solder, but this is exactly the arrangement needed to set up the breadboard as a jig for soldering. Place the headers lightly in the correct holes in the breadboard. Align the to insert into the Digispark and push it all home.
Tack the outer pins in place, then complete the soldering starting on the middle pins and ending with a reflow of the outer pins. Unlike the stapled boards where both rows of pins were clamping, the slight angle in this case does not cause trouble inserting or removing the board. We now have a Digispark that can be powered from the breadboard rails without pesky jumpers.
The installed Digispark. Note the slight angle of the board.
One of my concerns with this method was stressing the contacts inside the breadboard and making them unreliable. I tested this as best I could with multiple insertions and found no trouble when inserting jumpers and components in the same holes. I would say that it is probably important to make sure that your end result plugs in and removes easily because if not it would be an indicator of more stress and possible damage. I have come to consider these cheap breadboards as "reusable" but ultimately, consumable.
I hope this helps someone to have just a little nicer time with a Digispark on a breadboard, or possibly some other adaptation of the idea.
—————
1. It appears to the naïve eye there is room for one more pin along the edge and it would have been very nice to have GND show up there.
Designers of small boards often struggle with layout of the pins for headers. The limited real estate makes breaking out enough pins that are sill breadboard friendly very difficult. The Digispark (with USB port) is no exception.
The six pins along the edge are perfectly happy in a breadboard. However, the three others that wouldn't fit on the edge¹—5V, GND, and VIN are at right angles to them, and as you know on a breadboard the pins all have to run one way. If they don't, you can choose what to short out but something is going to be shorted. The usual thing is to choose what you want more in the breadboard and omit the header from the others, or install it topside. A right angle header is sometimes very helpful for that.
However, by a happy coincidence, the case of the Digispark provides and opportunity for a little hack, Its layout happens to almost match the holes in the board and the rails, which are common at 90° to the main board busses.
The fuscia lines indicate the common connections, the dashed line is the hole centers on the main board.
So we have the main busses at 90° to the rails, so that's good but as you can see from the dashed red line, the holes on the rails are, for some good reason one hopes, offset by about .05". The Digispark's pins are apparently laid out on an imaginary .1" grade over the entire board so that places the pins .05" out of alignment with the otherwise fortuitous fact that the rails are just in the right spot to match up with the 5V and GND pins.
If you solder the pins in properly and do a good job, the board just isn't going to fit. So what to do? Some people use a trick to solder headers that involves putting them in a breadboard as a sort of vise and soldering in place. I don't really like that method on two counts:
1. There is a real possibility of overheating and melting the breadboard, and while I have no proof of it, the not-so-robust construction of most breadboards leads me to suspect that even in the absence of a melty outcome the reliability of the heated holes in the board could be diminished.
2. I have found it is possible to have the pins at an angle and not know it until you attempt to extract the completed job from the board, only to find the pins are holding it in like staples. This is no fun to fix after you've managed to free it, particularly on boards with 10s of pins on each side.
But, it is that second bit that plays to our advantage in this case. The lesson learned from the "trick" is first of all, if you are going to do it, just tack in the end pins on each header, then finish out of the breadboard, and if for some reason you want angled pins, you can get them.
The tips of the pins are in the holes they will be pushed into, note the empirically achieved perfect angle.
As you can see in the photo, the pins for the rails are angled based on the actual insertion of the board. The photo is post-solder, but this is exactly the arrangement needed to set up the breadboard as a jig for soldering. Place the headers lightly in the correct holes in the breadboard. Align the to insert into the Digispark and push it all home.
Tack the outer pins in place, then complete the soldering starting on the middle pins and ending with a reflow of the outer pins. Unlike the stapled boards where both rows of pins were clamping, the slight angle in this case does not cause trouble inserting or removing the board. We now have a Digispark that can be powered from the breadboard rails without pesky jumpers.
The installed Digispark. Note the slight angle of the board.
I hope this helps someone to have just a little nicer time with a Digispark on a breadboard, or possibly some other adaptation of the idea.
—————
1. It appears to the naïve eye there is room for one more pin along the edge and it would have been very nice to have GND show up there.
