Roger Parkinson
Active member
Here's what I would like to build: a piggy back board for the Teensy3 which holds a microSD and a lipo charger circuit that feeds the Teensy3 with enough power (around 3.7-3.9 volts as measured in my prototype). I need something like this for the two projects I have (strictly hobby stuff) and it might be generally useful so if I can make it work I'll post the Eagle files. I don't have any ambitions to build these for sale, but if someone else does that's fine.
There seem to be two microSD holders available and the one Paul used for the Teensy 2.0 piggy back is smaller than the other, which is too wide to fit in the width of the Teensy3 (same as the width of the other Teensys actually) between the pins. Paul's piggy back board works well for the Teensy 2.0, is not quite so convenient for the Teensy++ 2.0 and doesn't match up too well at all with the Teensy 3. The part number for that microSD holder is HR1941CT-ND.
The second requirement of this is the lipo charger based on a MCP73831. It will take input voltage from the Teensy3's Vusb pin (which I rather rejoiced to see 'cos doing this on an earlier Teensy meant doing stuff with the solder pads and I usually screwed that up). It has a JST connector for the battery and a switch to kill the power going to the board, actually to the Vin pin on the Teensy 3.
Finally I figured since the microSD needs to use pins 10,11,12 and 13 my piggy back would cover the end of the Teensy3 including the push-button and I ought to put a second button to do the same thing, which just means a button that connects Program to GND. I do know there are other options for those pins but, if I read it right, they all involve using at least pin 13 or 14, both of which would need the end of the Teensy3 board covered. The other option is to drill an access hole in the piggy back board and save a little soldering. I'm still wondering about that.
I got the original charger circuit from asselinpaul.posterous.com (the design isn't on the web just now, a logistics thing, but they were happy to send it to me) and that is really a USB charger so my prototype on this consisted of sending the Eagle files to OSH, ordering some parts and then trying my hand at some SMD soldering. I was pretty surprised it worked actually 'cos I suck at soldering.
Next are the outstanding questions I have to resolve. Bear in mind this is the first time I've tried messing about with Eagle, I have hardly a clue what I'm doing, and my knowledge of electronics is pretty basic. I say this to encourage feedback. If you think I'm doing something dumb you are probably right and I'm happy to hear.
![piggyback-early.png piggyback-early.png](https://forum.pjrc.com/data/attachments/0/533-fd015690a1c3408a2105e65c11f9d741.jpg)
0) Is this worth doing? I have looked around for other solutions but if someone can tell me 'all you really need is...' then hearing that now rather than later is good.
1) Paul gives a diagram for his microSD design which uses an MCP1700 to handle a 5v supply. I don't need that for the Teensy3 'cos it is built in (the 3.3v pin, yay!) but I'm not sure if I need the 74LCX175 etc or not. The larger microSD is very simple, basically the pins go straight through and I tested that to see if it works on the Teensy3: it does. So I'm hoping the smaller one is just as simple, but then why did Paul add that 74LCX175? So this is a general question about wiring that microSD.
2) I found by experiment (and then I looked it up...) that the Teensy3 won't flash if it is given less than about 4v. Specifically it won't flash using the 3.9v coming from the charger circuit which is what I get when the USB is plugged in. My solution is to route the Vusb directly to Vin through a diode and I have Vin connected to the battery through a similar diode. I'm fairly sure this isn't the best way to do this, but I haven't thought of anything better.
3) I've attached my Eagle schematic. I'm feeling my way here and I've only a vague idea how to do the board layout. If there's anything I'm doing at this stage that I ought to change around I value the feedback.
Thanks for any help
Roger
There seem to be two microSD holders available and the one Paul used for the Teensy 2.0 piggy back is smaller than the other, which is too wide to fit in the width of the Teensy3 (same as the width of the other Teensys actually) between the pins. Paul's piggy back board works well for the Teensy 2.0, is not quite so convenient for the Teensy++ 2.0 and doesn't match up too well at all with the Teensy 3. The part number for that microSD holder is HR1941CT-ND.
The second requirement of this is the lipo charger based on a MCP73831. It will take input voltage from the Teensy3's Vusb pin (which I rather rejoiced to see 'cos doing this on an earlier Teensy meant doing stuff with the solder pads and I usually screwed that up). It has a JST connector for the battery and a switch to kill the power going to the board, actually to the Vin pin on the Teensy 3.
Finally I figured since the microSD needs to use pins 10,11,12 and 13 my piggy back would cover the end of the Teensy3 including the push-button and I ought to put a second button to do the same thing, which just means a button that connects Program to GND. I do know there are other options for those pins but, if I read it right, they all involve using at least pin 13 or 14, both of which would need the end of the Teensy3 board covered. The other option is to drill an access hole in the piggy back board and save a little soldering. I'm still wondering about that.
I got the original charger circuit from asselinpaul.posterous.com (the design isn't on the web just now, a logistics thing, but they were happy to send it to me) and that is really a USB charger so my prototype on this consisted of sending the Eagle files to OSH, ordering some parts and then trying my hand at some SMD soldering. I was pretty surprised it worked actually 'cos I suck at soldering.
Next are the outstanding questions I have to resolve. Bear in mind this is the first time I've tried messing about with Eagle, I have hardly a clue what I'm doing, and my knowledge of electronics is pretty basic. I say this to encourage feedback. If you think I'm doing something dumb you are probably right and I'm happy to hear.
![piggyback-early.png piggyback-early.png](https://forum.pjrc.com/data/attachments/0/533-fd015690a1c3408a2105e65c11f9d741.jpg)
0) Is this worth doing? I have looked around for other solutions but if someone can tell me 'all you really need is...' then hearing that now rather than later is good.
1) Paul gives a diagram for his microSD design which uses an MCP1700 to handle a 5v supply. I don't need that for the Teensy3 'cos it is built in (the 3.3v pin, yay!) but I'm not sure if I need the 74LCX175 etc or not. The larger microSD is very simple, basically the pins go straight through and I tested that to see if it works on the Teensy3: it does. So I'm hoping the smaller one is just as simple, but then why did Paul add that 74LCX175? So this is a general question about wiring that microSD.
2) I found by experiment (and then I looked it up...) that the Teensy3 won't flash if it is given less than about 4v. Specifically it won't flash using the 3.9v coming from the charger circuit which is what I get when the USB is plugged in. My solution is to route the Vusb directly to Vin through a diode and I have Vin connected to the battery through a similar diode. I'm fairly sure this isn't the best way to do this, but I haven't thought of anything better.
3) I've attached my Eagle schematic. I'm feeling my way here and I've only a vague idea how to do the board layout. If there's anything I'm doing at this stage that I ought to change around I value the feedback.
Thanks for any help
Roger