cp2104 schematic question - Page 1
Forum section: electronics / projects

author: Karamel
author_rank: Regular Contributor
timestamp: June 09, 2015, 03:31:06 am
content: hi everyone,i would like to ask a question about cp2104 schematic. in previous summer, i have been designed a usb to rs485 converter with cp2104. (you can see its schematics bellow) . passed too many days, and today, i can test my design. however, it didn't work. i have tried on two pcb. i am thinkig that, my schematic may be mistake. can you look at my schematic? is there any problem?best regards,karamel

author: stefanh
author_rank: Contributor
timestamp: June 09, 2015, 05:19:59 am
content: The schematic shows two USB to UART ICs. Are both the CP2104 and MCP2200 populated on the PCB?Where is the CP2104 getting its 3.3V power from? Are you supplying this externally?The design also seems to be missing a number of VCC decoupling capacitors.

author: Karamel
author_rank: Regular Contributor
timestamp: June 09, 2015, 09:04:03 am
content: Hi,Thanks for replying and sorry for my poor explaining.When i designed it, i want to two usb to uart ic. As you know this pcb's aim is teaching. Thus, i had a two ic and i have design it like this but only one ic can be used on pcb. First, i have been tried mcp2200. It worked but it is no allow to control rts cts pin with software. Rts, cts pins can be connected 75176's re and de pins. Therefore, pcb worked usb ttl converter but didnt work usb to rs485 control. Yesterday, i have tried with cp2104 but two pcb didn't work. Pc didin't find any usb-uart converter.I wanted to use usb power which is 5v so i used internal regulator of cp2104 like datasheet.Now, i am outside. When i come home, i will upload pcb photo and i will give more details.Best regarda,Karamel

author: codeboy2k
author_rank: Super Contributor
timestamp: June 09, 2015, 09:09:39 am
content: I cannot offer any more other than what's been said already.Tell us how it's not working. Have you checked all the voltages on the board? Show us the PCB.In addition, I'd like to point out that you have not drawn a schematic. You have placed a bunch of parts on the page.Don't draw your schematics like this. Connect the wires. Almost everything on the page has only one other place it connects to, so connect them, and make it a proper schematic.The Internet is making everyone draw stupid schematics like this.

author: stefanh
author_rank: Contributor
timestamp: June 09, 2015, 12:17:47 pm
content: I have not personally used this device. However I have contemplated doing a similar project.Is the VPP connection correct? The datasheet states "Connect a 4.7 µF capacitor between this pin and ground to support ROM programming via USB interface." The GPIO.2 pin is an input by default and you will need to configure the device to make it the RS485 Transceiver Control signal.Is the GND pad of the QFN soldered properly? The datasheet says that is optional, however I would want all my GND connections soldered.Follow the datasheet schematic diagram for all connections and component values exactly. Have you also double checked your footprint.Good Luck.

author: Karamel
author_rank: Regular Contributor
timestamp: June 09, 2015, 10:22:01 pm
content: Hi,Thanks for interesting.I have changed a little bit things on schematic for understanding better. Everything looks like on page 16 in datasheethttps://www.pololu.com/file/0J679/cp2104.pdfC4 is a decoupling capacitor for cp2104. Tomorrow, i will use 4.7uf instead of C4.Furthermore, I have taken some photo with my cheap(absolutely rubbish) microscope. I guess soldering is okay.and there is footprint. I have been checked two times it before i sent pcb manufacturing. it is looking okay is it?Now, I have no any voltmeter to measure voltages but i will measure them tomorrow. I am just wondering, is my schematic correct? or not?In conclusion, I am a high school student who is in 18 and i am not also attending vocational high school. Thus, I am learning electronics myself to myself. I know that, i can sometimes ask stupid question. It could be but i am learning with you....Thanks for allKaramel

author: Karamel
author_rank: Regular Contributor
timestamp: June 10, 2015, 11:51:47 pm
content: Hi,I measured all voltage on pcb.Vusb = 5v. Thus, Regin and VBus 5vI saw that, on chip regulator is working because, VIO and VDD have 3.2 voltage.Also, Vpp has a 3.1v but there is no any action. I have no any oscilloscope.Therefore, i can not see these voltages. I guess, i have a power problem. I am not still sure that is my schematic true or not?Best regards,Karamel