My Arduino clones

[dlh]

My Zarduino project is progressing. A distributor of Arduino related products has offered to help fund the development and then distribute everything once finished.

I am currently redesigning the Serial IO shield and, in the process, am adding a USB Host channel using a MAX3421E. For my specific project, I only need to support a single self-powered peripheral but for those who may want to use the boards with non-ZBasic chips and create their own firmware, I want to make it a bit more universal.

The problem is that I need the boards to work with 5V or 3.3V and a 3.3V supply presents problems as I need to supply +5V/300mA VBus for use with other USB peripherals. There are three MAX3232 RS232 chips on the same board but I don't think I can steal that much juice from them. I think I need to add a voltage doubler in order to supply VBus on a 3.3V system. I have attached a schematic of my USB Host setup with a 5V supply and another with 3.3V supply and unknown voltage doubler.

Can anyone recommend a chip I can use to supply +5V to the MAX4793 with a 3.3V system?

• http://davehouston.org/roZetta.htm
  http://davehouston.org/Arduino.htm

[spamiam]

Can anyone recommend a chip I can use to supply +5V to the MAX4793 with a 3.3V system?

How much space do you have? How much current do you need to supply?

Linear Technology makes a few options. The LTC3200 type looks good, but I have not used it personally. It uses relatively small value external caps, and comes in a fairly small package. It can tolerate a short of Vout. It is a switching type boost regulator, so you have to be careful about isolation and short traces.

What do you think about this one? Not exactly cheap.

-Tony

[dlh]

I don't expect space to be a limitation. As for current, I'm not sure - the device I want to support in my firmware is self-powered so all I need to do is sense voltage drops when a device is plugged in. However, I'd like to make this as universal as possible - the Arduino distributor would like my stuff to inter-operate with Arduino stuff. Jan Axelson tells me the OTG spec is for 8mA minimum with the maximum determined by the particular device.

I found a TI chip (TPS61200) that can do 600mA which is twice what the USB Host spec calls for (I think). The chip is 3mm² (soldering should be fun) but there are several caps/resistors. I haven't checked the price but SparkFun sells a LiPo to 3.3V device that uses a chip in the same family and they retail it for $5-6 so I think it might be affordable.

I'm hoping Jan Axelson's book on Embedded Hosts, due in November will help sort all this out. For now, I'm just trying to get the hardware right so I can order prototypes. The PCB also has five 8-pin PIC12F1822s and associated circuitry to handle five highspeed (115200) hardware USART based RS232 ports and an RS485 line driver w/timer for automatic line reversal and I want to get that working before tackling the USB.

[twesthoff]

Dave,
I am curious why you are using PIC processors for the serial ports.  Do you do something special with them? Or are they just cheaper than a multi-port hardware UART chip?
Tom W

On 10/6/2011 11:25 AM, General wrote:

I don't expect space to be a limitation. As for current, I'm not sure - the device I want to support in my firmware is self-powered so all I need to do is sense voltage drops when a device is plugged in. However, I'd like to make this as universal as possible - the Arduino distributor would like my stuff to inter-operate with Arduino stuff. Jan Axelson tells me the OTG spec is for 8mA minimum with the maximum determined by the particular device.

I found a TI chip (TPS61200) that can do 600mA which is twice what the USB Host spec calls for (I think). The chip is 3mm² (soldering should be fun) but there are several caps/resistors. I haven't checked the price but SparkFun sells a LiPo to 3.3V device that uses a chip in the same family and they retail it for $5-6 so I think it might be affordable.

I'm hoping Jan Axelson's book on Embedded Hosts, due in November will help sort all this out. For now, I'm just trying to get the hardware right so I can order prototypes. The PCB also has five 8-pin PIC12F1822s and associated circuitry to handle five highspeed (115200) hardware USART based RS232 ports and an RS485 line driver w/timer for automatic line reversal and I want to get that working before tackling the USB.



davehouston.org

[spamiam]

I found a TI chip (TPS61200) that can do 600mA which is twice what the USB Host spec calls for (I think). The chip is 3mm² (soldering should be fun) but there are several caps/resistors. I haven't checked the price but SparkFun sells a LiPo to 3.3V device that uses a chip in the same family and they retail it for $5-6 so I think it might be affordable.

I think that the only good way to use a DFN package is reflow soldering. The power pad under the chip certainly cant be soldered by hand unless you use a big via underneath. I have no experience with that package, nor reflow, so I cant say for sure. I sure wouldn't want to try to solder that one! Without soldering the power pad, the device probably would not be able to sustain the full rated current output.

The TPS61200 requires some relatively high value caps, and an inductor. It is $3.90 in single units from Digikey.

The LT device I mentioned previously is no more expensive, and easier to solder, and doesn't need an inductor, and uses lower value caps. It will probably be easier and cheaper to use. The LT device is good for 90 or 100mA, which might be good enough for OTG.

-Tony

[dlh]

I am curious why you are using PIC processors for the serial ports. Do you do something special with them? Or are they just cheaper than a multi-port hardware UART chip?

I'm not sure what you mean by multi-port hardware UART chip. But, to answer your question, it could be that I don't know any better.

The latest PICs have accurate internal oscillators and hardware EUSARTs. In this case, they run independent of the system processor and pass data to/from the system processor over I2C (hardware based on both ends). The PICs can also do hardware based SPI. The PICs cost about $1 each plus (3) MAX3232 RS232C line driver ICs and cost is a major consideration.

On another shield I'm using the same approach for 8 channels of pulse-stream IO (i.e. RF/IR RX/TX) and 8 ADC/DIO channels. Two 8-pin PICs and two 14-pin PICs with DIP sockets so users can only add what they need. In the unlikely event that someone needs more serial ports, I can use software UARTs in these PICs for 0-5V RS232. On the serial shield, there's insufficient space for sockets.

In my application, messages are infrequent so this is overkill but I'm trying to reach a wider audience.

[dlh]

I think that the only good way to use a DFN package is reflow soldering. The power pad under the chip certainly cant be soldered by hand unless you use a big via underneath. I have no experience with that package, nor reflow, so I cant say for sure.

Reflow is easier than using a soldering iron, especially if you have a stencil to apply the paste. I've done a lot in a $50 Black & Decker convection oven.

This, I'll have to do without a stencil but I think I can handle it. If not, it might be worth a stencil - it can always go to the people who will be doing the production assembly. I'll let the distributor decide.

This is not an OTG application so I'd rather have the higher current. Also, I'm designing to use either 3V3 or 5V but not both as some Arduino designs offer. Power comes from SMPS wallwarts. The extra current capacity might come in handy to power a 5V device in a 3V3 system.

The biggest problem is getting too much paste on the big pad - that tends to float the chip and mess up alignment and the other contacts.