MX1508 versus MX1508RX - Page 1
Forum section: electronics / projects

author: pcprogrammer
author_rank: Super Contributor
timestamp: January 30, 2024, 02:44:31 pm
content: Quite a while back I ordered MX1508 motor driver ic's on aliexpress but at the time did not got round to testing them. Couple days back I received the PCB's I designed for my fischertechnik remote control project and soldered, what I thought to be, the MX1508's on the board. While pre power measuring the connections I noticed on one of the two ic's a very low resistance between what I assume to be the motor voltage input and a control pin. Also found that one of the alleged motor output pins has a dead short with the same assumed motor voltage input pin.I checked a loose ic and there it showed the same dead short, but not the low resistance between the two adjacent pins. I looked at the marking on the ic and noticed it to be MX1508RX, where as on the modules, I also bought from aliexpress, have MX1508 as marking on the ic's.I was able to find a datasheet for the MX1508, which is translated from Chinese and used that together with the modules as a basis for my design. Even used the modules in the prototype and all works fine.My new board on the other hand shorts the power supply. Removed a MX1508 from one of the modules I have, and soldered a MX1508RX onto it, and to no surprise that also shorts out the power supply. Have yet to try the de-soldered MX1508 on my new board. Removing the ferrite beads in the motor power supply to the MX1508RX's solves the short and the rest of the board seems to work.So now I wonder what the actual difference between the two is. Either I got aliexpressed and the ic's are fake as hell or the pinout is different and then the big question is, how it is different.Searching on google showed me that there are suppliers who offer them both and you can choose which one to buy.Any one on the forum who used these MX1508RX ones?

author: pcprogrammer
author_rank: Super Contributor
timestamp: January 30, 2024, 04:57:03 pm
content: De-soldered two MX1508's from module boards and placed them on my new board. Works as intended, so I at least have a working receiver for my project to keep on going.Ordered an other bunch of MX1508's from aliexpress and hope they turn out to be the correct ones.

author: pcprogrammer
author_rank: Super Contributor
timestamp: January 31, 2024, 03:18:44 pm
content: I found out that the IC's I took from the module boards most likely are also knockoffs. They have 1508S as marking on them, and did not live to long on my new PCB. In the prototype the modules have actual MX1508's on them based on the markings on the IC's and they work, but with a big motor that needs a lot of startup current it needs the supply voltage to be high enough to get the motor turning, otherwise it stalls. Not sure if this is due to internal current limiting.A bit of a bummer because it needs to work with this motor and a 6V battery supply voltage.The 1508S IC's died when I was testing with this big motor and 8.6V supply voltage. Quick on and off switching at full power caused one IC to become a short and the other only works in one direction on the first channel. The second channel is still working.Also the MCU went of in unknown code territory several times. A timer interrupt kept on going though.Time for a bit of a redesign.

author: pcprogrammer
author_rank: Super Contributor
timestamp: April 05, 2024, 06:47:24 am
content: I again received a batch of MX1508RX while I ordered MX1508, so started a dispute and got my money back.Could not resist to do another search on the net to find more information on it, and it might be that the RX version has some special receiver support in it to directly work with a signal from a transmitter / receiver without the need for a MCU.Need to research it a bit more by translating a text I found on thiswebsite. The site does not allow translate nor copy and paste of the text on my Firefox browser so I'm doing it bit by bit from the HTML source.The chip diagram does show some consistency with continuity between pins I measured on the chip. Pins 4, 8 and 9 are connected to each other and all marked as ground. (Be it AGND and PGND, but ground non the less)I can try it with some voltage connected to see if there is the 2.5V output from the internal LDO. That would make it more certain that I'm on the right path.

author: pcprogrammer
author_rank: Super Contributor
timestamp: April 05, 2024, 12:14:33 pm
content: Unfortunately there is no 2.5V on pin 13 when I connect > 6V to pin 12 and GND to pin 4.I did measure a connection between pin 5 and 12, which are both VM in the diagram I found. It also looks like that I can measure the body diodes of the output FET's on the given pins. DMM + lead on pin 9 and DMM com lead on pin 10 shows a diode, other way round it is infinite, same on pin 10 and similar on pin 9 to pin 12, etc.Connecting a supply to pin 13 has no current draw as long as Vsupply is < ~3V. After that it starts to draw current to about 75mA at 3.2V or so.So it remains a bit of a mystery as to what this IC is.Maybe the MX1508RX2 is yet another derivative of the original MX1508 and has the RX2 protocol support, but than what is the RX version.

author: pcprogrammer
author_rank: Super Contributor
timestamp: April 06, 2024, 11:00:34 am
content: Short update on the MX1508RX.I connected 2.5V to pin 13 and ground to pin 4 and noticed that it has indeed two inverters in the package.Input pinOutput pin1415161For further testing I have to hook it up to an Arduino nano and try it with some sketches I found for generating RX2 control data. According to somedatasheetI found it is possible to have 5 controls. This includes turbo, so I guess pin 3 marked turbo is an output to control a gear or something to increase the speed.What I found so far indicates that it is basically used for remote controlled toy cars.Also attached the found PDF here so it does not get lost.